diff --git a/functions/src/add-bounty.ts b/functions/src/add-bounty.ts
new file mode 100644
index 00000000..2f5dee11
--- /dev/null
+++ b/functions/src/add-bounty.ts
@@ -0,0 +1,53 @@
+import * as admin from 'firebase-admin'
+import { z } from 'zod'
+
+import { Contract } from '../../common/contract'
+import { User } from '../../common/user'
+import { APIError, newEndpoint, validate } from './api'
+
+const firestore = admin.firestore()
+
+const bodySchema = z.object({
+  contractId: z.string(),
+  amount: z.number().gt(0),
+})
+
+export const addbounty = newEndpoint({}, async (req, auth) => {
+  const { amount, contractId } = validate(bodySchema, req.body)
+
+  return await firestore.runTransaction(async (transaction) => {
+    const userDoc = firestore.doc(`users/${auth.uid}`)
+    const userSnap = await transaction.get(userDoc)
+    if (!userSnap.exists) throw new APIError(400, 'User not found')
+    const user = userSnap.data() as User
+
+    const contractDoc = firestore.doc(`contracts/${contractId}`)
+    const contractSnap = await transaction.get(contractDoc)
+    if (!contractSnap.exists) throw new APIError(400, 'Invalid contract')
+    const contract = contractSnap.data() as Contract
+    if (contract.outcomeType !== 'BOUNTY')
+      throw new APIError(400, "Can't add bounties to non-BOUNTY contracts")
+
+    const { closeTime } = contract
+    if (closeTime && Date.now() > closeTime)
+      throw new APIError(400, 'Contract is closed')
+
+    if (user.balance < amount) throw new APIError(400, 'Insufficient balance')
+
+    transaction.update(userDoc, {
+      balance: user.balance - amount,
+      totalDeposits: user.totalDeposits - amount,
+    })
+
+    const existingPrize = contract.prizes[user.id] ?? 0
+
+    transaction.update(contractDoc, {
+      prizes: {
+        ...contract.prizes,
+        [user.id]: existingPrize + amount,
+      },
+    })
+
+    return { status: 'success' }
+  })
+})
diff --git a/functions/src/index.ts b/functions/src/index.ts
index 07b37648..5e83ac6f 100644
--- a/functions/src/index.ts
+++ b/functions/src/index.ts
@@ -66,6 +66,7 @@ import { stripewebhook, createcheckoutsession } from './stripe'
 import { getcurrentuser } from './get-current-user'
 import { acceptchallenge } from './accept-challenge'
 import { getcustomtoken } from './get-custom-token'
+import { addbounty } from './add-bounty'
 
 const toCloudFunction = ({ opts, handler }: EndpointDefinition) => {
   return onRequest(opts, handler as any)
@@ -91,6 +92,7 @@ const createCheckoutSessionFunction = toCloudFunction(createcheckoutsession)
 const getCurrentUserFunction = toCloudFunction(getcurrentuser)
 const acceptChallenge = toCloudFunction(acceptchallenge)
 const getCustomTokenFunction = toCloudFunction(getcustomtoken)
+const addBountyFunction = toCloudFunction(addbounty)
 
 export {
   healthFunction as health,
@@ -114,4 +116,5 @@ export {
   getCurrentUserFunction as getcurrentuser,
   acceptChallenge as acceptchallenge,
   getCustomTokenFunction as getcustomtoken,
+  addBountyFunction as addbounty,
 }
diff --git a/functions/src/serve.ts b/functions/src/serve.ts
index bf96db20..85066cd0 100644
--- a/functions/src/serve.ts
+++ b/functions/src/serve.ts
@@ -27,6 +27,7 @@ import { unsubscribe } from './unsubscribe'
 import { stripewebhook, createcheckoutsession } from './stripe'
 import { getcurrentuser } from './get-current-user'
 import { getcustomtoken } from './get-custom-token'
+import { addbounty } from './add-bounty'
 
 type Middleware = (req: Request, res: Response, next: NextFunction) => void
 const app = express()
@@ -65,6 +66,7 @@ addJsonEndpointRoute('/resolvemarket', resolvemarket)
 addJsonEndpointRoute('/unsubscribe', unsubscribe)
 addJsonEndpointRoute('/createcheckoutsession', createcheckoutsession)
 addJsonEndpointRoute('/getcurrentuser', getcurrentuser)
+addJsonEndpointRoute('/addbounty', addbounty)
 addEndpointRoute('/getcustomtoken', getcustomtoken)
 addEndpointRoute('/stripewebhook', stripewebhook, express.raw())
 
diff --git a/web/lib/firebase/api.ts b/web/lib/firebase/api.ts
index 5f250ce7..0dcf0dd3 100644
--- a/web/lib/firebase/api.ts
+++ b/web/lib/firebase/api.ts
@@ -88,3 +88,7 @@ export function acceptChallenge(params: any) {
 export function getCurrentUser(params: any) {
   return call(getFunctionUrl('getcurrentuser'), 'GET', params)
 }
+
+export function addBounty(params: any) {
+  return call(getFunctionUrl('addbounty'), 'POST', params)
+}