diff --git a/Gemfile b/Gemfile
index 863d16f..21e78cf 100644
--- a/Gemfile
+++ b/Gemfile
@@ -88,3 +88,5 @@ group :test do
   # Code coverage; started in test/test_helper.rb only when COVERAGE=1
   gem "simplecov", require: false
 end
+
+gem "money-rails", "~> 3.0"
diff --git a/Gemfile.lock b/Gemfile.lock
index ecea679..2a19f5b 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -226,6 +226,16 @@ GEM
     minitest (6.0.6)
       drb (~> 2.0)
       prism (~> 1.5)
+    monetize (2.0.0)
+      money (~> 7.0)
+    money (7.1.1)
+      bigdecimal
+      i18n (~> 1.9)
+    money-rails (3.0.0)
+      activesupport (>= 7.0)
+      monetize (~> 2.0)
+      money (~> 7.0)
+      railties (>= 7.0)
     msgpack (1.8.4)
     net-imap (0.6.6)
       date
@@ -489,6 +499,7 @@ DEPENDENCIES
   json (>= 2.21.2)
   kamal
   letter_opener
+  money-rails (~> 3.0)
   nokogiri (>= 1.19.4)
   postmark-rails (~> 0.22)
   propshaft
@@ -597,6 +608,9 @@ CHECKSUMS
   mini_magick (5.3.1) sha256=29395dfd76badcabb6403ee5aff6f681e867074f8f28ce08d78661e9e4a351c4
   mini_mime (1.1.5) sha256=8681b7e2e4215f2a159f9400b5816d85e9d8c6c6b491e96a12797e798f8bccef
   minitest (6.0.6) sha256=153ea36d1d987a62942382b61075745042a2b3123b1cd48f4c3675af9cc7d6f1
+  monetize (2.0.0) sha256=152980cadff9fd11a95817d56e3d7d69b07998c4506f15d971edf05851f82aba
+  money (7.1.1) sha256=8ed5cd99dfbc45e82688ea711cb59ea3c396c2608cd88876502b164c90269d4e
+  money-rails (3.0.0) sha256=f4bd1c8e1c98d221e7bf452eeb52e240f41224e43da2a477a5659a87c0c95bae
   msgpack (1.8.4) sha256=4411c22d350dd1c20250f7eada3cca2695438c2f769cf0782f0cd065d90a3e7b
   net-imap (0.6.6) sha256=96aa4ee50df3060203e649efc341f53480b791d49e150f2fdebf68beb141a8df
   net-pop (0.1.2) sha256=848b4e982013c15b2f0382792268763b748cce91c9e91e36b0f27ed26420dff3
diff --git a/app/models/allocation.rb b/app/models/allocation.rb
index e5cc0f8..c449ec6 100644
--- a/app/models/allocation.rb
+++ b/app/models/allocation.rb
@@ -1,4 +1,6 @@
 class Allocation < ApplicationRecord
+  monetize :amount_cents, allow_nil: true
+
   belongs_to :scenario
   belongs_to :allocation_category, optional: true
 
diff --git a/app/models/allocation/one_time.rb b/app/models/allocation/one_time.rb
index d81eee1..386dafa 100644
--- a/app/models/allocation/one_time.rb
+++ b/app/models/allocation/one_time.rb
@@ -1,5 +1,5 @@
 class Allocation::OneTime < Allocation
-  validates :amount,
+  validates :amount_cents,
     presence: true,
     numericality: { only_integer: true, greater_than: 0 }
   validate :within_total_giving_amount
@@ -16,7 +16,7 @@ def share_percentage
     total = scenario.one_time_giving_amount
     return 0 if total.zero?
 
-    (amount.to_i / total.to_f * 100).round
+    (amount.cents / total.cents.to_f * 100).round
   end
 
   # The most this allocation can be set to while staying within the scenario's
@@ -34,21 +34,18 @@ def max_amount(scenario = self.scenario)
   private
 
   def within_total_giving_amount
-    return if amount.blank? || scenario&.total_giving_amount.blank?
+    return if amount_cents.blank? || scenario&.total_giving_amount_cents.blank?
 
-    remaining = budget_remaining(scenario)
-    return if remaining.nil?
-
-    if amount > remaining
-      others = scenario.total_giving_amount - remaining
-      errors.add(:amount, "would bring one-time giving to #{others + amount}, over the total giving amount of #{scenario.total_giving_amount.to_i}")
+    others = scenario.one_time_allocations.where.not(id: id).sum(:amount_cents)
+    if others + amount_cents > scenario.total_giving_amount_cents
+      errors.add(:amount, "would bring one-time giving to #{(others + amount_cents) / 100.0}, over the total giving amount of #{(scenario.total_giving_amount_cents / 100.0).to_i}")
     end
   end
 
   def budget_remaining(scenario = self.scenario)
     return nil if scenario.blank? || scenario.total_giving_amount.blank?
 
-    others = scenario.one_time_allocations.where.not(id: id).sum(:amount)
-    scenario.total_giving_amount - others
+    others = scenario.one_time_allocations.where.not(id: id).sum(:amount_cents)
+    (scenario.total_giving_amount_cents - others) / 100
   end
 end
diff --git a/app/models/allocation/ongoing.rb b/app/models/allocation/ongoing.rb
index 35335bd..c44789a 100644
--- a/app/models/allocation/ongoing.rb
+++ b/app/models/allocation/ongoing.rb
@@ -7,11 +7,11 @@ class Allocation::Ongoing < Allocation
   validate :within_ongoing_percentage_total
 
   def dollar_amount
-    (percentage.to_i / 100.0 * scenario.ongoing_giving_amount).round
+    scenario.ongoing_giving_amount * (percentage.to_i / 100.0)
   end
 
   def perpetuity_annual_amount
-    (dollar_amount * PERPETUITY_PAYOUT_RATE).round
+    dollar_amount * PERPETUITY_PAYOUT_RATE
   end
 
   def ongoing?
diff --git a/app/models/scenario.rb b/app/models/scenario.rb
index 1c69ede..300d8a7 100644
--- a/app/models/scenario.rb
+++ b/app/models/scenario.rb
@@ -1,6 +1,8 @@
 class Scenario < ApplicationRecord
   include UserSearchable
 
+  monetize :total_giving_amount_cents, allow_nil: true
+
   belongs_to :organization
   belongs_to :user
   has_many :allocations, dependent: :destroy
@@ -33,11 +35,11 @@ def ongoing_percentage_total
   end
 
   def one_time_giving_amount
-    one_time_allocations.sum { |allocation| allocation.amount.to_i }
+    one_time_allocations.sum(Money.new(0)) { |allocation| allocation.amount }
   end
 
   def ongoing_giving_amount
-    total_giving_amount.to_i - one_time_giving_amount
+    (total_giving_amount || Money.new(0)) - one_time_giving_amount
   end
 
   private
diff --git a/app/views/admin/scenarios/index.html.erb b/app/views/admin/scenarios/index.html.erb
index 92b7394..38affea 100644
--- a/app/views/admin/scenarios/index.html.erb
+++ b/app/views/admin/scenarios/index.html.erb
@@ -41,7 +41,7 @@
               </td>
               <td class="px-4 py-2.5 text-right tabular-nums text-ink">
                 <%= link_to scenario_path(scenario), data: { turbo_frame: "_top" }, class: "block" do %>
-                  <%= scenario.total_giving_amount.present? ? number_to_currency(scenario.total_giving_amount, precision: 0) : content_tag(:span, "—", class: "text-ink-faint") %>
+                  <%= scenario.total_giving_amount.present? ? number_to_currency(scenario.total_giving_amount) : content_tag(:span, "—", class: "text-ink-faint") %>
                 <% end %>
               </td>
             </tr>
diff --git a/app/views/public/scenarios/show.html.erb b/app/views/public/scenarios/show.html.erb
index aa1237a..35b9026 100644
--- a/app/views/public/scenarios/show.html.erb
+++ b/app/views/public/scenarios/show.html.erb
@@ -6,9 +6,9 @@
   <div class="mt-6">
     <h1 class="font-serif font-medium text-3xl text-ink"><%= @scenario.name %></h1>
     <p class="mt-1 text-sm text-ink-soft">Shared by <span class="font-medium text-ink"><%= @scenario.user.display_name %></span></p>
-    <% if @scenario.total_giving_amount.to_i.positive? %>
+    <% if @scenario.total_giving_amount&.positive? %>
       <p class="mt-3 text-ink-soft">
-        Total giving <span class="font-medium text-ink"><%= number_to_currency(@scenario.total_giving_amount, precision: 0) %></span>
+        Total giving <span class="font-medium text-ink"><%= number_to_currency(@scenario.total_giving_amount) %></span>
       </p>
     <% end %>
   </div>
diff --git a/app/views/scenarios/_allocation.html.erb b/app/views/scenarios/_allocation.html.erb
index d3e8082..b09fa82 100644
--- a/app/views/scenarios/_allocation.html.erb
+++ b/app/views/scenarios/_allocation.html.erb
@@ -4,7 +4,7 @@
   <% slider_limit = remaining_ongoing_percentage(scenario, allocation) %>
   <div data-controller="dialog">
     <div data-controller="allocation-slider"
-         data-allocation-slider-ongoing-amount-value="<%= scenario.ongoing_giving_amount %>"
+         data-allocation-slider-ongoing-amount-value="<%= scenario.ongoing_giving_amount.to_i %>"
          data-allocation-slider-payout-rate-value="<%= Allocation::Ongoing::PERPETUITY_PAYOUT_RATE %>"
          data-allocation-slider-limit-value="<%= slider_limit %>"
          class="rounded-lg border <%= allocation.greatest_community_need? ? "border-brand/30 bg-brand-tint" : "border-line-soft bg-surface" %> px-4 py-3 transition hover:shadow-sm">
@@ -25,7 +25,7 @@
         <div class="flex items-start gap-3 shrink-0">
           <div class="w-16 text-right leading-tight">
             <span class="block font-semibold text-ink tabular-nums" data-allocation-slider-target="percent"><%= allocation.percentage %>%</span>
-            <span class="block text-sm text-ink-faint tabular-nums" data-allocation-slider-target="dollar"><%= number_to_currency(allocation.dollar_amount, precision: 0) %></span>
+            <span class="block text-sm text-ink-faint tabular-nums" data-allocation-slider-target="dollar"><%= number_to_currency(allocation.dollar_amount) %></span>
           </div>
           <% unless allocation.greatest_community_need? %>
             <button type="button" data-action="dialog#open" aria-label="Edit allocation"
@@ -59,13 +59,13 @@
         <% end %>
         <div class="flex items-baseline gap-3 shrink-0">
           <span class="w-10 text-right font-semibold text-ink tabular-nums" data-allocation-slider-target="percent"><%= allocation.percentage %>%</span>
-          <span class="w-16 text-right text-ink-soft tabular-nums" data-allocation-slider-target="dollar"><%= number_to_currency(allocation.dollar_amount, precision: 0) %></span>
+          <span class="w-16 text-right text-ink-soft tabular-nums" data-allocation-slider-target="dollar"><%= number_to_currency(allocation.dollar_amount) %></span>
         </div>
       </div>
 
       <p class="mt-3 text-xs text-ink-faint">
         <span style="color: <%= color %>">&infin;</span>
-        Est. <span class="font-medium text-ink-soft" data-allocation-slider-target="perpetuity"><%= number_to_currency(allocation.perpetuity_annual_amount, precision: 0) %></span>
+        Est. <span class="font-medium text-ink-soft" data-allocation-slider-target="perpetuity"><%= number_to_currency(allocation.perpetuity_annual_amount) %></span>
         annually in perpetuity
         <span class="text-ink-faint">(<%= (Allocation::Ongoing::PERPETUITY_PAYOUT_RATE * 100).to_i %>% of principal)</span>
       </p>
@@ -89,7 +89,7 @@
       </div>
       <div class="flex items-center gap-3 shrink-0">
         <span class="font-semibold text-ink">
-          <%= number_to_currency(allocation.amount, precision: 0) %>
+          <%= number_to_currency(allocation.amount) %>
         </span>
         <button type="button" data-action="dialog#open"
                 class="text-sm text-ink-faint hover:text-accent cursor-pointer bg-transparent p-0 leading-none">
diff --git a/app/views/scenarios/_allocation_modal.html.erb b/app/views/scenarios/_allocation_modal.html.erb
index 2d6aca2..e03f985 100644
--- a/app/views/scenarios/_allocation_modal.html.erb
+++ b/app/views/scenarios/_allocation_modal.html.erb
@@ -33,7 +33,7 @@
         <%= label_tag "allocation_amount_#{suffix}", "Amount", class: "block text-sm text-ink-soft" %>
         <div class="relative mt-1">
           <span class="absolute left-3 top-1/2 -translate-y-1/2 text-ink-faint">$</span>
-          <%= number_field_tag "allocation[amount]", allocation.amount, id: "allocation_amount_#{suffix}", min: 0, max: max_amount, step: "1", required: true, placeholder: "0",
+          <%= number_field_tag "allocation[amount]", allocation.amount.to_i, id: "allocation_amount_#{suffix}", min: 0, max: max_amount, step: "1", required: true, placeholder: "0",
                 inputmode: "numeric",
                 data: max_amount.present? ? { controller: "integer-input one-time-amount", action: "input->integer-input#transform", one_time_amount_max_value: max_amount } : { controller: "integer-input", action: "input->integer-input#transform" },
                 class: "block w-full rounded-md border border-line bg-surface pl-7 pr-3 py-2 shadow-sm focus:border-accent focus:outline-none focus:ring-2 focus:ring-accent/10" %>
diff --git a/app/views/scenarios/_summary.html.erb b/app/views/scenarios/_summary.html.erb
index 39cdb22..3600845 100644
--- a/app/views/scenarios/_summary.html.erb
+++ b/app/views/scenarios/_summary.html.erb
@@ -1,15 +1,15 @@
 <%# locals: (scenario:) %>
-<% ongoing_total    = scenario.ongoing_percentage_total %>
-<% ongoing_amount   = scenario.ongoing_giving_amount %>
-<% one_time_amount  = scenario.one_time_giving_amount %>
-<% total_amount     = scenario.total_giving_amount.to_i %>
+<% ongoing_total  = scenario.ongoing_percentage_total %>
+<% ongoing_amount = scenario.ongoing_giving_amount %>
+<% one_time_amount = scenario.one_time_giving_amount %>
+<% total_amount   = scenario.total_giving_amount %>
 <div class="rounded-2xl border border-line bg-surface p-6 shadow-sm">
   <h2 class="font-serif font-medium text-xl text-ink">Allocation summary</h2>
-  <% if total_amount.positive? %>
+  <% if total_amount.present? && total_amount.positive? %>
     <p class="mt-2 text-sm text-ink-soft">
-      Ongoing <span class="font-medium text-brand"><%= number_to_currency(ongoing_amount, precision: 0) %></span>
-      + One-time <span class="font-medium text-ink"><%= number_to_currency(one_time_amount, precision: 0) %></span>
-      = Total <span class="font-medium text-ink"><%= number_to_currency(total_amount, precision: 0) %></span>
+      Ongoing <span class="font-medium text-brand"><%= number_to_currency(ongoing_amount) %></span>
+      + One-time <span class="font-medium text-ink"><%= number_to_currency(one_time_amount) %></span>
+      = Total <span class="font-medium text-ink"><%= number_to_currency(total_amount) %></span>
     </p>
   <% else %>
     <p class="mt-2 text-sm text-ink-soft">Set your total above to see a full breakdown.</p>
@@ -17,7 +17,7 @@
 
   <div class="mt-5">
     <h3 class="text-[11px] font-semibold uppercase tracking-wide text-ink-faint">Ongoing giving</h3>
-    <p class="mt-1 font-serif text-4xl font-medium text-ink"><%= number_to_currency(ongoing_amount, precision: 0) %></p>
+    <p class="mt-1 font-serif text-4xl font-medium text-ink"><%= number_to_currency(ongoing_amount) %></p>
     <% if scenario.ongoing_allocations.any? %>
       <p class="mt-1 text-sm text-ink-soft">
         <%= ongoing_total %>% allocated across <%= pluralize(scenario.ongoing_allocations.count, "cause") %>
@@ -72,11 +72,11 @@
               </span>
               <span class="flex items-baseline gap-3">
                 <span class="font-medium text-ink"><%= allocation.percentage %>%</span>
-                <span class="text-ink-soft"><%= number_to_currency(allocation.dollar_amount, precision: 0) %></span>
+                <span class="text-ink-soft"><%= number_to_currency(allocation.dollar_amount) %></span>
               </span>
             </div>
             <p class="ml-[18px] mt-0.5 text-xs text-ink-faint">
-              &infin; Est. <%= number_to_currency(allocation.perpetuity_annual_amount, precision: 0) %> /yr in perpetuity
+              &infin; Est. <%= number_to_currency(allocation.perpetuity_annual_amount) %> /yr in perpetuity
             </p>
           </li>
         <% end %>
@@ -93,7 +93,7 @@
           One time giving
           <span class="rounded border border-line px-1.5 py-0.5 text-[10px] font-medium tracking-normal text-ink-soft">ADD-ON</span>
         </h3>
-        <span class="font-medium text-ink"><%= number_to_currency(one_time_amount, precision: 0) %></span>
+<span class="font-medium text-ink"><%= number_to_currency(one_time_amount) %></span>
       </div>
       <ul class="mt-3 space-y-2">
         <% scenario.one_time_allocations.each do |allocation| %>
@@ -104,7 +104,7 @@
             </span>
             <span class="flex items-baseline gap-3">
               <span class="font-medium text-ink-soft"><%= allocation.share_percentage %>%</span>
-              <span class="text-ink-soft"><%= number_to_currency(allocation.amount, precision: 0) %></span>
+              <span class="text-ink-soft"><%= number_to_currency(allocation.amount) %></span>
             </span>
           </li>
         <% end %>
@@ -112,11 +112,11 @@
     </div>
   <% end %>
 
-  <% if total_amount.positive? %>
+  <% if total_amount.present? && total_amount.positive? %>
     <div class="mt-6 rounded-xl border border-line bg-surface-soft p-4 text-sm text-ink-soft">
-      Ongoing <span class="font-medium text-brand"><%= number_to_currency(ongoing_amount, precision: 0) %></span>
-      + One-time <span class="font-medium text-ink"><%= number_to_currency(one_time_amount, precision: 0) %></span>
-      = Total <span class="font-medium text-ink"><%= number_to_currency(total_amount, precision: 0) %></span>
+      Ongoing <span class="font-medium text-brand"><%= number_to_currency(ongoing_amount) %></span>
+      + One-time <span class="font-medium text-ink"><%= number_to_currency(one_time_amount) %></span>
+      = Total <span class="font-medium text-ink"><%= number_to_currency(total_amount) %></span>
     </div>
   <% end %>
 </div>
diff --git a/app/views/scenarios/index.html.erb b/app/views/scenarios/index.html.erb
index 946b7d3..19c2e58 100644
--- a/app/views/scenarios/index.html.erb
+++ b/app/views/scenarios/index.html.erb
@@ -19,7 +19,7 @@
             <%= link_to scenario.name, scenario_path(scenario), class: "font-serif font-medium text-lg text-ink hover:text-brand" %>
           </div>
           <p class="mt-2 text-ink-soft">
-            <%= scenario.total_giving_amount.present? ? number_to_currency(scenario.total_giving_amount, precision: 0) : "No total set" %>
+            <%= scenario.total_giving_amount.present? ? number_to_currency(scenario.total_giving_amount) : "No total set" %>
           </p>
           <div class="mt-4 flex items-center gap-3 text-sm">
             <%= link_to "Open", scenario_path(scenario), class: "text-brand hover:underline" %>
diff --git a/app/views/scenarios/total_giving_amounts/_form.html.erb b/app/views/scenarios/total_giving_amounts/_form.html.erb
index 103723a..51fe458 100644
--- a/app/views/scenarios/total_giving_amounts/_form.html.erb
+++ b/app/views/scenarios/total_giving_amounts/_form.html.erb
@@ -6,9 +6,8 @@
       <%= form.label :total_giving_amount, "Total giving amount", class: "w-40 text-ink-soft" %>
       <div class="relative max-w-md w-full">
         <span class="absolute left-3 top-1/2 -translate-y-1/2 text-ink-faint">$</span>
-        <%= form.number_field :total_giving_amount, step: "1", min: 0, autofocus: true, placeholder: "0",
-              inputmode: "numeric",
-              data: { controller: "integer-input", action: "input->integer-input#transform" },
+        <%= form.number_field :total_giving_amount, value: scenario.total_giving_amount&.to_i, step: "1", min: 0, autofocus: true, placeholder: "0",
+              inputmode: "decimal",
               class: "block w-full rounded-md border border-line bg-surface-soft pl-7 pr-3 py-2 shadow-sm focus:border-accent focus:outline-none focus:ring-2 focus:ring-accent/10" %>
       </div>
 
diff --git a/app/views/scenarios/total_giving_amounts/_total_giving_amount.html.erb b/app/views/scenarios/total_giving_amounts/_total_giving_amount.html.erb
index 6f59843..5463890 100644
--- a/app/views/scenarios/total_giving_amounts/_total_giving_amount.html.erb
+++ b/app/views/scenarios/total_giving_amounts/_total_giving_amount.html.erb
@@ -5,7 +5,7 @@
       <span class="w-40 text-ink-soft">Total giving amount</span>
       <% if scenario.total_giving_amount.present? %>
         <%= link_to edit_scenario_total_giving_amount_path(scenario), class: "group inline-flex items-center gap-2" do %>
-          <span class="font-medium text-ink"><%= number_to_currency(scenario.total_giving_amount, precision: 0) %></span>
+          <span class="font-medium text-ink"><%= number_to_currency(scenario.total_giving_amount) %></span>
           <span class="text-ink-faint opacity-0 transition group-hover:opacity-100" aria-hidden="true">
             <svg class="h-5 w-5" fill="none" viewBox="0 0 24 24" stroke="currentColor" stroke-width="2">
               <path stroke-linecap="round" stroke-linejoin="round" d="M16.862 4.487l1.687-1.688a1.875 1.875 0 112.652 2.652L10.582 16.07a4.5 4.5 0 01-1.897 1.13L6 18l.8-2.685a4.5 4.5 0 011.13-1.897l8.932-8.931z" />
diff --git a/config/initializers/money.rb b/config/initializers/money.rb
new file mode 100644
index 0000000..b0627e4
--- /dev/null
+++ b/config/initializers/money.rb
@@ -0,0 +1,22 @@
+# encoding : utf-8
+
+MoneyRails.configure do |config|
+  # Monetary amounts in this app are always USD, stored as integer cents in
+  # `_cents` columns.
+  config.default_currency = :usd
+
+  # Use whole-dollar formatting (no cents) for display in views.
+  config.no_cents_if_whole = true
+end
+
+# Make `number_to_currency` delegate to the money gem whenever it receives a
+# Money object, so display formatting (currency, no_cents_if_whole) is handled
+# by Money instead of Rails' numeric formatter.
+module MoneyNumberToCurrency
+  def number_to_currency(number, options = {})
+    return number.format(options) if number.is_a?(Money)
+
+    super
+  end
+end
+ActionView::Helpers::NumberHelper.prepend(MoneyNumberToCurrency)
diff --git a/db/migrate/20260829000000_store_amounts_in_cents.rb b/db/migrate/20260829000000_store_amounts_in_cents.rb
new file mode 100644
index 0000000..2dbe1b4
--- /dev/null
+++ b/db/migrate/20260829000000_store_amounts_in_cents.rb
@@ -0,0 +1,17 @@
+class StoreAmountsInCents < ActiveRecord::Migration[8.1]
+  def up
+    rename_column :scenarios, :total_giving_amount, :total_giving_amount_cents
+    rename_column :allocations, :amount, :amount_cents
+
+    execute "UPDATE scenarios SET total_giving_amount_cents = total_giving_amount_cents * 100"
+    execute "UPDATE allocations SET amount_cents = amount_cents * 100"
+  end
+
+  def down
+    execute "UPDATE scenarios SET total_giving_amount_cents = total_giving_amount_cents / 100"
+    execute "UPDATE allocations SET amount_cents = amount_cents / 100"
+
+    rename_column :scenarios, :total_giving_amount_cents, :total_giving_amount
+    rename_column :allocations, :amount_cents, :amount
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 1ed32e7..882b503 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.1].define(version: 2026_08_28_183247) do
+ActiveRecord::Schema[8.1].define(version: 2026_08_29_000000) do
   create_table "active_storage_attachments", force: :cascade do |t|
     t.bigint "blob_id", null: false
     t.datetime "created_at", null: false
@@ -63,7 +63,7 @@
 
   create_table "allocations", force: :cascade do |t|
     t.integer "allocation_category_id"
-    t.integer "amount"
+    t.integer "amount_cents"
     t.datetime "created_at", null: false
     t.text "note"
     t.string "option"
@@ -100,7 +100,7 @@
     t.string "name", null: false
     t.integer "organization_id", null: false
     t.string "share_token"
-    t.integer "total_giving_amount"
+    t.integer "total_giving_amount_cents"
     t.datetime "updated_at", null: false
     t.integer "user_id", null: false
     t.index ["organization_id"], name: "index_scenarios_on_organization_id"
diff --git a/test/controllers/allocations_controller_test.rb b/test/controllers/allocations_controller_test.rb
index 9ebd078..d020e8b 100644
--- a/test/controllers/allocations_controller_test.rb
+++ b/test/controllers/allocations_controller_test.rb
@@ -134,7 +134,7 @@ class AllocationsControllerTest < ActionDispatch::IntegrationTest
       allocation: { amount: 4000 }
     }
     assert_redirected_to scenario_path(@scenario)
-    assert_equal 4000, allocation.reload.amount
+    assert_equal 400_000, allocation.reload.amount_cents
   end
 
   test "rejects an update that exceeds the total giving amount" do
@@ -145,7 +145,7 @@ class AllocationsControllerTest < ActionDispatch::IntegrationTest
     }
     assert_redirected_to scenario_path(@scenario)
     assert flash[:alert].present?
-    assert_equal 5000, allocation.reload.amount
+    assert_equal 500_000, allocation.reload.amount_cents
   end
 
   test "cannot update an allocation on a scenario you do not own" do
diff --git a/test/controllers/scenarios/total_giving_amounts_controller_test.rb b/test/controllers/scenarios/total_giving_amounts_controller_test.rb
index 2c84f95..ca29548 100644
--- a/test/controllers/scenarios/total_giving_amounts_controller_test.rb
+++ b/test/controllers/scenarios/total_giving_amounts_controller_test.rb
@@ -23,7 +23,7 @@ class Scenarios::TotalGivingAmountsControllerTest < ActionDispatch::IntegrationT
   test "update changes the total giving amount" do
     patch scenario_total_giving_amount_url(@scenario), params: { scenario: { total_giving_amount: 5000 } }
     assert_response :success
-    assert_equal 5000, @scenario.reload.total_giving_amount
+    assert_equal 500_000, @scenario.reload.total_giving_amount_cents
   end
 
   test "update responds with turbo_stream that replaces the total and allocations frames" do
@@ -49,7 +49,7 @@ class Scenarios::TotalGivingAmountsControllerTest < ActionDispatch::IntegrationT
 
     patch scenario_total_giving_amount_url(@scenario), params: { scenario: { total_giving_amount: 7500 } }
     assert_response :success
-    assert_equal 7500, @scenario.reload.total_giving_amount
+    assert_equal 750_000, @scenario.reload.total_giving_amount_cents
   end
 
   test "plain member cannot edit another user's scenario total in the same org" do
diff --git a/test/controllers/scenarios_controller_test.rb b/test/controllers/scenarios_controller_test.rb
index c5084be..129e862 100644
--- a/test/controllers/scenarios_controller_test.rb
+++ b/test/controllers/scenarios_controller_test.rb
@@ -48,7 +48,7 @@ class ScenariosControllerTest < ActionDispatch::IntegrationTest
 
   test "update changes total giving amount" do
     patch scenario_url(scenarios(:one_arlington)), params: { scenario: { total_giving_amount: 2500 } }
-    assert_equal 2500, scenarios(:one_arlington).reload.total_giving_amount
+    assert_equal 250_000, scenarios(:one_arlington).reload.total_giving_amount_cents
   end
 
   test "destroy removes the scenario" do
@@ -74,7 +74,7 @@ class ScenariosControllerTest < ActionDispatch::IntegrationTest
   test "admin can update another user's scenario" do
     sign_in_as users(:admin)
     patch scenario_url(scenarios(:one_arlington)), params: { scenario: { total_giving_amount: 999 } }
-    assert_equal 999, scenarios(:one_arlington).reload.total_giving_amount
+    assert_equal 99_900, scenarios(:one_arlington).reload.total_giving_amount_cents
   end
 
   test "admin destroy of another user's scenario returns to the admin dashboard" do
@@ -101,6 +101,6 @@ class ScenariosControllerTest < ActionDispatch::IntegrationTest
     sign_in_as users(:super_admin)
     patch scenario_url(scenarios(:one_arlington)), params: { scenario: { total_giving_amount: 1 } }
     assert_response :not_found
-    assert_equal 10000, scenarios(:one_arlington).reload.total_giving_amount
+    assert_equal 1_000_000, scenarios(:one_arlington).reload.total_giving_amount_cents
   end
 end
diff --git a/test/fixtures/allocations.yml b/test/fixtures/allocations.yml
index d299b0d..030d5ef 100644
--- a/test/fixtures/allocations.yml
+++ b/test/fixtures/allocations.yml
@@ -10,4 +10,4 @@ education_grant:
   scenario: one_arlington
   type: Allocation::OneTime
   allocation_category: program_education
-  amount: 5000
+  amount_cents: 500000
diff --git a/test/fixtures/scenarios.yml b/test/fixtures/scenarios.yml
index 001d51d..7385545 100644
--- a/test/fixtures/scenarios.yml
+++ b/test/fixtures/scenarios.yml
@@ -2,16 +2,16 @@ one_arlington:
   user: one
   organization: arlington
   name: Scenario 1
-  total_giving_amount: 10000
+  total_giving_amount_cents: 1000000
 
 admin_arlington:
   user: admin
   organization: arlington
   name: Admin plan
-  total_giving_amount: 25000
+  total_giving_amount_cents: 2500000
 
 two_boston:
   user: two
   organization: boston
   name: Boston plan
-  total_giving_amount: 5000
+  total_giving_amount_cents: 500000
diff --git a/test/models/allocation/ongoing_test.rb b/test/models/allocation/ongoing_test.rb
index c0302b2..76b7919 100644
--- a/test/models/allocation/ongoing_test.rb
+++ b/test/models/allocation/ongoing_test.rb
@@ -1,11 +1,23 @@
 require "test_helper"
 
 class Allocation::OngoingTest < ActiveSupport::TestCase
-  test "dollar_amount is the percentage of ongoing giving" do
-    assert_equal 1500, allocations(:greatest_need).dollar_amount
+  test "dollar_amount is the percentage of ongoing giving in cents" do
+    assert_equal Money.new(150_000), allocations(:greatest_need).dollar_amount
   end
 
-  test "perpetuity_annual_amount is 5% of the dollar amount" do
-    assert_equal 75, allocations(:greatest_need).perpetuity_annual_amount
+  test "perpetuity_annual_amount is 5% of the dollar amount in cents" do
+    assert_equal Money.new(7_500), allocations(:greatest_need).perpetuity_annual_amount
+  end
+
+  test "retains cents when percentage math produces a sub-dollar amount" do
+    scenario = Scenario.new(organization: organizations(:arlington), user: users(:one), name: "Cents plan")
+    scenario.total_giving_amount = 100
+    scenario.save!
+    scenario.one_time_allocations.delete_all
+
+    allocation = scenario.ongoing_allocations.create!(option: "X", percentage: 33)
+
+    assert_equal Money.new(3_300), allocation.dollar_amount
+    assert_equal Money.new(165), allocation.perpetuity_annual_amount
   end
 end
diff --git a/test/models/allocation_test.rb b/test/models/allocation_test.rb
index 3b15fde..2b56288 100644
--- a/test/models/allocation_test.rb
+++ b/test/models/allocation_test.rb
@@ -54,9 +54,9 @@ class AllocationTest < ActiveSupport::TestCase
     assert_not allocation.update(percentage: 101)
   end
 
-  test "ongoing dollar_amount is its percentage of the scenario's ongoing giving" do
+  test "ongoing dollar_amount is its percentage of the scenario's ongoing giving in cents" do
     # scenario ongoing giving is 10000 total - 5000 one-time = 5000; greatest_need is 30%.
-    assert_equal 1500, allocations(:greatest_need).dollar_amount
+    assert_equal Money.new(150_000), allocations(:greatest_need).dollar_amount
   end
 
   test "preference_categories can be assigned and destroying the allocation removes the join rows" do
diff --git a/test/models/scenario_test.rb b/test/models/scenario_test.rb
index 0a59e17..c7b137d 100644
--- a/test/models/scenario_test.rb
+++ b/test/models/scenario_test.rb
@@ -17,17 +17,17 @@ class ScenarioTest < ActiveSupport::TestCase
     assert_equal 30, scenarios(:one_arlington).ongoing_percentage_total
   end
 
-  test "one_time_giving_amount sums one-time allocation amounts" do
-    assert_equal 5000, scenarios(:one_arlington).one_time_giving_amount
+  test "one_time_giving_amount sums one-time allocation amounts in cents" do
+    assert_equal Money.new(500_000), scenarios(:one_arlington).one_time_giving_amount
   end
 
-  test "ongoing_giving_amount is total giving minus one-time gifts" do
-    assert_equal 5000, scenarios(:one_arlington).ongoing_giving_amount
+  test "ongoing_giving_amount is total giving minus one-time gifts in cents" do
+    assert_equal Money.new(500_000), scenarios(:one_arlington).ongoing_giving_amount
   end
 
   test "ongoing_giving_amount treats a missing total as zero" do
     scenario = Scenario.new
-    assert_equal 0, scenario.ongoing_giving_amount
+    assert_equal 0, scenario.ongoing_giving_amount.cents
   end
 
   test "destroys dependent allocations" do