diff --git a/services/web/app/src/Features/Subscription/PlansHelper.mjs b/services/web/app/src/Features/Subscription/PlansHelper.mjs
index fa310a9316..8647b35270 100644
--- a/services/web/app/src/Features/Subscription/PlansHelper.mjs
+++ b/services/web/app/src/Features/Subscription/PlansHelper.mjs
@@ -15,7 +15,20 @@ export function isProfessionalGroupPlan(subscription) {
   return subscription.groupPlan && isProfessional
 }
 
+/**
+ * The per-month price shown when a plan or add-on is billed annually: the
+ * annual price divided by twelve, rounded up to the nearest 0.05 for a tidy
+ * display value.
+ *
+ * @param {number} annual
+ * @returns {number}
+ */
+export function roundedTwelfth(annual) {
+  return Math.round(Math.ceil(annual / 12 / 0.05) * 5) / 100
+}
+
 export default {
   isProfessionalPlan,
   isProfessionalGroupPlan,
+  roundedTwelfth,
 }
diff --git a/services/web/test/unit/src/Project/ProjectController.test.mjs b/services/web/test/unit/src/Project/ProjectController.test.mjs
index 35ef2693e0..1e7cb8e496 100644
--- a/services/web/test/unit/src/Project/ProjectController.test.mjs
+++ b/services/web/test/unit/src/Project/ProjectController.test.mjs
@@ -43,7 +43,6 @@ describe('ProjectController', function () {
           collaborator: {
             monthly: 15,
             annual: 180,
-            annualDividedByTwelve: 15,
           },
         },
       },
@@ -1602,7 +1601,6 @@ describe('ProjectController', function () {
             assistant: {
               annual: 60,
               monthly: 5,
-              annualDividedByTwelve: 5,
             },
           },
         }
diff --git a/services/web/test/unit/src/Subscription/PlansHelper.test.mjs b/services/web/test/unit/src/Subscription/PlansHelper.test.mjs
new file mode 100644
index 0000000000..bcdee76b8e
--- /dev/null
+++ b/services/web/test/unit/src/Subscription/PlansHelper.test.mjs
@@ -0,0 +1,18 @@
+import { describe, expect, it } from 'vitest'
+import { roundedTwelfth } from '../../../../app/src/Features/Subscription/PlansHelper.mjs'
+
+describe('PlansHelper', function () {
+  describe('roundedTwelfth', function () {
+    it('divides by twelve when the result is already a multiple of 0.05', function () {
+      expect(roundedTwelfth(120)).to.equal(10)
+      expect(roundedTwelfth(180)).to.equal(15)
+    })
+
+    it('rounds up to the nearest 0.05 for display', function () {
+      // 263 / 12 = 21.9166… -> 21.95
+      expect(roundedTwelfth(263)).to.equal(21.95)
+      // 505 / 12 = 42.0833… -> 42.1
+      expect(roundedTwelfth(505)).to.equal(42.1)
+    })
+  })
+})