diff --git a/common/contract.ts b/common/contract.ts
index 6e362de0..8aad82fe 100644
--- a/common/contract.ts
+++ b/common/contract.ts
@@ -21,6 +21,8 @@ export type FullContract<
 
   createdTime: number // Milliseconds since epoch
   lastUpdatedTime: number // If the question or description was changed
+  lastBetTime?: number
+  lastCommentTime?: number
   closeTime?: number // When no more trading is allowed
 
   isResolved: boolean
diff --git a/functions/src/index.ts b/functions/src/index.ts
index d87e88f9..004a22b0 100644
--- a/functions/src/index.ts
+++ b/functions/src/index.ts
@@ -12,6 +12,7 @@ export * from './create-contract'
 export * from './create-user'
 export * from './create-fold'
 export * from './create-answer'
+export * from './on-create-bet'
 export * from './on-create-comment'
 export * from './on-fold-follow'
 export * from './on-fold-delete'
diff --git a/functions/src/on-create-bet.ts b/functions/src/on-create-bet.ts
new file mode 100644
index 00000000..12e6e720
--- /dev/null
+++ b/functions/src/on-create-bet.ts
@@ -0,0 +1,27 @@
+import * as functions from 'firebase-functions'
+import * as admin from 'firebase-admin'
+import * as _ from 'lodash'
+
+import { getContract } from './utils'
+import { Bet } from '../../common/bet'
+
+const firestore = admin.firestore()
+
+export const onCreateBet = functions.firestore
+  .document('contracts/{contractId}/bets/{betId}')
+  .onCreate(async (change, context) => {
+    const { contractId } = context.params as {
+      contractId: string
+    }
+
+    const contract = await getContract(contractId)
+    if (!contract)
+      throw new Error('Could not find contract corresponding with bet')
+
+    const bet = change.data() as Bet
+
+    await firestore
+      .collection('contracts')
+      .doc(contract.id)
+      .update({ lastBetTime: bet.createdTime })
+  })
diff --git a/functions/src/on-create-comment.ts b/functions/src/on-create-comment.ts
index 02ade1fe..d232e2ed 100644
--- a/functions/src/on-create-comment.ts
+++ b/functions/src/on-create-comment.ts
@@ -18,12 +18,18 @@ export const onCreateComment = functions.firestore
     }
 
     const contract = await getContract(contractId)
-    if (!contract) return
+    if (!contract)
+      throw new Error('Could not find contract corresponding with comment')
 
     const comment = change.data() as Comment
 
     const commentCreator = await getUser(comment.userId)
-    if (!commentCreator) return
+    if (!commentCreator) throw new Error('Could not find contract creator')
+
+    await firestore
+      .collection('contracts')
+      .doc(contract.id)
+      .update({ lastCommentTime: comment.createdTime })
 
     let bet: Bet | undefined
     let answer: Answer | undefined