diff --git a/test/api/unit/libs/payments/stripe/calculate-termination-date.test.js b/test/api/unit/libs/payments/stripe/calculate-termination-date.test.js
new file mode 100644
index 0000000000..7badd7e62a
--- /dev/null
+++ b/test/api/unit/libs/payments/stripe/calculate-termination-date.test.js
@@ -0,0 +1,64 @@
+import moment from 'moment';
+import { calculateSubscriptionTerminationDate } from '../../../../../../website/server/libs/payments/util';
+import api from '../../../../../../website/server/libs/payments/payments';
+
+describe('#calculateSubscriptionTerminationDate', () => {
+  let plan;
+  let nextBill;
+
+  beforeEach(() => {
+    plan = {
+      customerId: 'customer-id',
+      extraMonths: 0,
+    };
+    nextBill = moment();
+  });
+  it('should extend date to the exact amount of days left before the next bill will occur', () => {
+    nextBill = moment()
+      .add(5, 'days');
+    const expectedTerminationDate = moment()
+      .add(5, 'days');
+
+    const terminationDate = calculateSubscriptionTerminationDate(nextBill, plan, api.constants);
+    expect(expectedTerminationDate.diff(terminationDate, 'days')).to.eql(0);
+  });
+  it('if nextBill is null, add 30 days to termination date', () => {
+    nextBill = null;
+    const expectedTerminationDate = moment()
+      .add(30, 'days');
+    const terminationDate = calculateSubscriptionTerminationDate(nextBill, plan, api.constants);
+
+    expect(expectedTerminationDate.diff(terminationDate, 'days')).to.eql(0);
+  });
+  it('if nextBill is null and it\'s a group plan, add 2 days instead of 30', () => {
+    nextBill = null;
+    plan.customerId = api.constants.GROUP_PLAN_CUSTOMER_ID;
+    const expectedTerminationDate = moment()
+      .add(2, 'days');
+
+    const terminationDate = calculateSubscriptionTerminationDate(nextBill, plan, api.constants);
+    expect(expectedTerminationDate.diff(terminationDate, 'days')).to.eql(0);
+  });
+  it('should add 30.5 days for each extraMonth', () => {
+    plan.extraMonths = 4;
+    const expectedTerminationDate = moment()
+      .add(30.5 * 4, 'days');
+
+    const terminationDate = calculateSubscriptionTerminationDate(nextBill, plan, api.constants);
+    expect(expectedTerminationDate.diff(terminationDate, 'days')).to.eql(0);
+  });
+  it('should round up if total days gained by extraMonth is a decimal number', () => {
+    plan.extraMonths = 5;
+    const expectedTerminationDate = moment()
+      .add(Math.ceil(30.5 * 5), 'days');
+
+    const terminationDate = calculateSubscriptionTerminationDate(nextBill, plan, api.constants);
+    expect(expectedTerminationDate.diff(terminationDate, 'days')).to.eql(0);
+  });
+  it('behaves like extraMonths is 0 if it\'s set to a negative number', () => {
+    plan.extraMonths = -5;
+    const expectedTerminationDate = moment();
+    const terminationDate = calculateSubscriptionTerminationDate(nextBill, plan, api.constants);
+    expect(expectedTerminationDate.diff(terminationDate, 'days')).to.eql(0);
+  });
+});
diff --git a/website/server/libs/payments/subscriptions.js b/website/server/libs/payments/subscriptions.js
index 96acf3451e..0f6d938d30 100644
--- a/website/server/libs/payments/subscriptions.js
+++ b/website/server/libs/payments/subscriptions.js
@@ -17,6 +17,7 @@ import {
 } from '../errors';
 import shared from '../../../common';
 import { sendNotification as sendPushNotification } from '../pushNotifications';
+import { calculateSubscriptionTerminationDate } from './util';
 
 // @TODO: Abstract to shared/constant
 const JOINED_GROUP_PLAN = 'joined group plan';
@@ -309,24 +310,11 @@ async function cancelSubscription (data) {
     if (data.cancellationReason && data.cancellationReason === JOINED_GROUP_PLAN) sendEmail = false;
   }
 
-  const now = moment();
-  let defaultRemainingDays = 30;
-
   if (plan.customerId === this.constants.GROUP_PLAN_CUSTOMER_ID) {
-    defaultRemainingDays = 2;
     sendEmail = false; // because group-member-cancel email has already been sent
   }
 
-  const remaining = data.nextBill ? moment(data.nextBill).diff(new Date(), 'days', true) : defaultRemainingDays;
-  if (plan.extraMonths < 0) plan.extraMonths = 0;
-  const extraDays = Math.ceil(30.5 * plan.extraMonths);
-  const nowStr = `${now.format('MM')}/${now.format('DD')}/${now.format('YYYY')}`;
-  const nowStrFormat = 'MM/DD/YYYY';
-
-  plan.dateTerminated = moment(nowStr, nowStrFormat)
-    .add({ days: remaining })
-    .add({ days: extraDays })
-    .toDate();
+  plan.dateTerminated = calculateSubscriptionTerminationDate(data.nextBill, plan, this.constants);
 
   // clear extra time. If they subscribe again, it'll be recalculated from p.dateTerminated
   plan.extraMonths = 0;
diff --git a/website/server/libs/payments/util.js b/website/server/libs/payments/util.js
new file mode 100644
index 0000000000..fb6b65daaa
--- /dev/null
+++ b/website/server/libs/payments/util.js
@@ -0,0 +1,32 @@
+import moment from 'moment';
+
+const DEFAULT_REMAINING_DAYS = 30;
+const DEFAULT_REMAINING_DAYS_FOR_GROUP_PLAN = 2;
+
+/**
+ * paymentsApiConstants is provided as parameter because of a dependency cycle
+ * with subscriptions api which will occur if api.constants would be used directly
+ */
+export function calculateSubscriptionTerminationDate (
+  nextBill, purchasedPlan, paymentsApiConstants,
+) {
+  const defaultRemainingDays = (
+    purchasedPlan.customerId === paymentsApiConstants.GROUP_PLAN_CUSTOMER_ID
+  ) ? DEFAULT_REMAINING_DAYS_FOR_GROUP_PLAN
+    : DEFAULT_REMAINING_DAYS;
+  const now = moment();
+
+  const remaining = nextBill
+    ? moment(nextBill).diff(new Date(), 'days', true)
+    : defaultRemainingDays;
+
+  const extraMonths = Math.max(purchasedPlan.extraMonths, 0);
+  const extraDays = Math.ceil(30.5 * extraMonths);
+  const nowStr = `${now.format('MM')}/${now.format('DD')}/${now.format('YYYY')}`;
+  const nowStrFormat = 'MM/DD/YYYY';
+
+  return moment(nowStr, nowStrFormat)
+    .add({ days: remaining })
+    .add({ days: extraDays })
+    .toDate();
+}