diff --git a/common/contract.ts b/common/contract.ts
index ecad95bd..82a330b5 100644
--- a/common/contract.ts
+++ b/common/contract.ts
@@ -20,6 +20,7 @@ export type FullContract<
   visibility: 'public' | 'unlisted'
 
   createdTime: number // Milliseconds since epoch
+  lastUpdatedTime?: number // Updated on new bet or comment
   lastBetTime?: number
   lastCommentTime?: number
   closeTime?: number // When no more trading is allowed
diff --git a/functions/src/on-create-bet.ts b/functions/src/on-create-bet.ts
index 12e6e720..deaa4c4a 100644
--- a/functions/src/on-create-bet.ts
+++ b/functions/src/on-create-bet.ts
@@ -19,9 +19,10 @@ export const onCreateBet = functions.firestore
       throw new Error('Could not find contract corresponding with bet')
 
     const bet = change.data() as Bet
+    const lastBetTime = bet.createdTime
 
     await firestore
       .collection('contracts')
       .doc(contract.id)
-      .update({ lastBetTime: bet.createdTime })
+      .update({ lastBetTime, lastUpdatedTime: Date.now() })
   })
diff --git a/functions/src/on-create-comment.ts b/functions/src/on-create-comment.ts
index d232e2ed..18fc6757 100644
--- a/functions/src/on-create-comment.ts
+++ b/functions/src/on-create-comment.ts
@@ -22,6 +22,7 @@ export const onCreateComment = functions.firestore
       throw new Error('Could not find contract corresponding with comment')
 
     const comment = change.data() as Comment
+    const lastCommentTime = comment.createdTime
 
     const commentCreator = await getUser(comment.userId)
     if (!commentCreator) throw new Error('Could not find contract creator')
@@ -29,7 +30,7 @@ export const onCreateComment = functions.firestore
     await firestore
       .collection('contracts')
       .doc(contract.id)
-      .update({ lastCommentTime: comment.createdTime })
+      .update({ lastCommentTime, lastUpdatedTime: Date.now() })
 
     let bet: Bet | undefined
     let answer: Answer | undefined