diff --git a/src/components/profile/subscription/SubscribeModal.js b/src/components/profile/subscription/SubscribeModal.js
index dcc36cb..6c5dd33 100644
--- a/src/components/profile/subscription/SubscribeModal.js
+++ b/src/components/profile/subscription/SubscribeModal.js
@@ -18,6 +18,7 @@ import NostrIcon from '../../../../public/images/nostr.png';
 import Image from 'next/image';
 import RenewSubscription from '@/components/profile/subscription/RenewSubscription';
 import { SelectButton } from 'primereact/selectbutton';
+import { calculateExpirationDate } from '@/constants/subscriptionPeriods';
 
 const SubscribeModal = ({ user }) => {
   const { data: session, update } = useSession();
@@ -45,13 +46,20 @@ const SubscribeModal = ({ user }) => {
     if (user && user.role) {
       setSubscribed(user.role.subscribed);
       setSubscriptionType(user.role.subscriptionType || 'monthly');
-      const subscribedAt = new Date(user.role.lastPaymentAt);
       
-      // Calculate subscription end date based on type
-      const daysToAdd = subscriptionType === 'yearly' ? 365 : 31;
-      const subscribedUntil = new Date(subscribedAt.getTime() + daysToAdd * 24 * 60 * 60 * 1000);
+      // Only calculate dates if lastPaymentAt exists
+      if (user.role.lastPaymentAt) {
+        const subscribedAt = new Date(user.role.lastPaymentAt);
+        
+        // Use the shared helper to calculate expiration date
+        const subscribedUntil = calculateExpirationDate(subscribedAt, subscriptionType);
+        
+        setSubscribedUntil(subscribedUntil);
+      } else {
+        // Reset the subscribedUntil value if no lastPaymentAt
+        setSubscribedUntil(null);
+      }
       
-      setSubscribedUntil(subscribedUntil);
       if (user.role.subscriptionExpiredAt) {
         const expiredAt = new Date(user.role.subscriptionExpiredAt);
         setSubscriptionExpiredAt(expiredAt);
@@ -174,7 +182,7 @@ const SubscribeModal = ({ user }) => {
             <Message className="w-fit" severity="success" text="Subscribed!" />
             <p className="mt-3">Thank you for your support 🎉</p>
             <p className="text-sm text-gray-400">
-              Pay-as-you-go {user?.role?.subscriptionType || 'monthly'} subscription will renew on {subscribedUntil?.toLocaleDateString()}
+              Pay-as-you-go {user?.role?.subscriptionType || 'monthly'} subscription will renew on {subscribedUntil ? subscribedUntil.toLocaleDateString() : 'N/A'}
             </p>
           </div>
         )}
@@ -183,7 +191,7 @@ const SubscribeModal = ({ user }) => {
             <Message className="w-fit" severity="success" text="Subscribed!" />
             <p className="mt-3">Thank you for your support 🎉</p>
             <p className="text-sm text-gray-400">
-              Recurring {user?.role?.subscriptionType || 'monthly'} subscription will AUTO renew on {subscribedUntil?.toLocaleDateString()}
+              Recurring {user?.role?.subscriptionType || 'monthly'} subscription will AUTO renew on {subscribedUntil ? subscribedUntil.toLocaleDateString() : 'N/A'}
             </p>
           </div>
         )}
diff --git a/src/constants/subscriptionPeriods.js b/src/constants/subscriptionPeriods.js
new file mode 100644
index 0000000..76e5f45
--- /dev/null
+++ b/src/constants/subscriptionPeriods.js
@@ -0,0 +1,36 @@
+// Constants for subscription periods to maintain consistency across the application
+export const SUBSCRIPTION_PERIODS = {
+  MONTHLY: {
+    DAYS: 30,
+    BUFFER_HOURS: 1, // Buffer time for expiration checks
+  },
+  YEARLY: {
+    DAYS: 365,
+    BUFFER_HOURS: 1, // Buffer time for expiration checks
+  }
+};
+
+// Helper to calculate expiration date (for UI display)
+export const calculateExpirationDate = (startDate, subscriptionType) => {
+  const periodDays = subscriptionType === 'yearly' 
+    ? SUBSCRIPTION_PERIODS.YEARLY.DAYS 
+    : SUBSCRIPTION_PERIODS.MONTHLY.DAYS;
+  
+  return new Date(startDate.getTime() + periodDays * 24 * 60 * 60 * 1000);
+};
+
+// Helper to check if subscription has expired (for backend logic)
+export const hasSubscriptionExpired = (lastPaymentDate, subscriptionType) => {
+  if (!lastPaymentDate) return true;
+  
+  const now = new Date();
+  const period = subscriptionType === 'yearly' 
+    ? SUBSCRIPTION_PERIODS.YEARLY 
+    : SUBSCRIPTION_PERIODS.MONTHLY;
+  
+  const expirationTime = lastPaymentDate.getTime() + 
+    (period.DAYS * 24 * 60 * 60 * 1000) + 
+    (period.BUFFER_HOURS * 60 * 60 * 1000);
+  
+  return now.getTime() > expirationTime;
+}; 
\ No newline at end of file
diff --git a/src/db/models/userModels.js b/src/db/models/userModels.js
index dd97c4e..1f97e91 100644
--- a/src/db/models/userModels.js
+++ b/src/db/models/userModels.js
@@ -1,4 +1,5 @@
 import prisma from '../prisma';
+import { SUBSCRIPTION_PERIODS } from '@/constants/subscriptionPeriods';
 
 export const getAllUsers = async () => {
   return await prisma.user.findMany({
@@ -205,12 +206,16 @@ export const findExpiredSubscriptions = async () => {
   try {
     const now = new Date();
     
-    // Define expiration periods
+    // Use the constants for expiration periods
     const monthlyExpiration = new Date(
-      now.getTime() - 30 * 24 * 60 * 60 * 1000 - 1 * 60 * 60 * 1000
+      now.getTime() - 
+      (SUBSCRIPTION_PERIODS.MONTHLY.DAYS * 24 * 60 * 60 * 1000) - 
+      (SUBSCRIPTION_PERIODS.MONTHLY.BUFFER_HOURS * 60 * 60 * 1000)
     );
     const yearlyExpiration = new Date(
-      now.getTime() - 365 * 24 * 60 * 60 * 1000 - 1 * 60 * 60 * 1000
+      now.getTime() - 
+      (SUBSCRIPTION_PERIODS.YEARLY.DAYS * 24 * 60 * 60 * 1000) - 
+      (SUBSCRIPTION_PERIODS.YEARLY.BUFFER_HOURS * 60 * 60 * 1000)
     );
 
     // Find expired subscriptions of both types