diff --git a/backend/src/index.ts b/backend/src/index.ts
index f5f5a7da..4283a243 100644
--- a/backend/src/index.ts
+++ b/backend/src/index.ts
@@ -11,6 +11,7 @@ import { beacon } from "./analytics.js";
 import { graniteLink } from "./granite.js";
 import { search } from "./spotify.js";
 import { getAudio, getImage } from "./storage.js";
+import { calculateStreak } from "./streak.js";
 
 const app = express();
 initializeApp({
@@ -69,6 +70,7 @@ app.post("/getImage", getImage);
 app.post("/getAudio", getAudio);
 
 app.post("/gap", gapFund);
+app.post("/streak", calculateStreak);
 app.post("/spotify/search", search);
 
 app.use(Sentry.Handlers.errorHandler());
diff --git a/backend/src/streak.ts b/backend/src/streak.ts
new file mode 100644
index 00000000..be547aaf
--- /dev/null
+++ b/backend/src/streak.ts
@@ -0,0 +1,71 @@
+import { getDatabase } from "firebase-admin/database";
+import { AnyMap, UserRequest, validateKeys } from "./helpers.js";
+import { Response } from "express";
+import { DateTime } from "luxon";
+import AES from "crypto-js/aes.js";
+import aesutf8 from "crypto-js/enc-utf8.js";
+
+const FETCH_LIMIT = 100;
+
+export const calculateStreak = async (req: UserRequest, res: Response) => {
+    const db = getDatabase();
+    const data = req.body;
+    const encryptionKey = await validateKeys(data.keys, db, req.user!.user_id);
+
+    if (!encryptionKey) {
+        res.sendStatus(400);
+        return;
+    }
+
+    const today = DateTime.fromISO(data.currentDate);
+    if (!data.currentDate || typeof data.currentDate !== "string" || !today.isValid) {
+        res.sendStatus(400);
+        return;
+    }
+
+    const logRef = db.ref(req.user!.user_id + "/logs").orderByKey();
+    let logs: AnyMap = await (await logRef.limitToLast(FETCH_LIMIT).get()).val();
+    if (!logs || Object.keys(logs).length === 0) {
+        res.send({ streak: 0, danger: false });
+        return;
+    }
+
+    let latestLog: AnyMap = JSON.parse(AES.decrypt(logs[Object.keys(logs).at(-1)!].data, encryptionKey).toString(aesutf8));
+    let top = DateTime.fromObject({ year: latestLog.year, month: latestLog.month, day: latestLog.day });
+
+    // If the top log is not today or yesterday, the streak is 0
+    if (top.toISODate() !== today.toISODate() && top.toISODate() !== today.minus({ days: 1 }).toISODate()) {
+        res.send({ streak: 0, danger: false });
+        return;
+    }
+    // If the top log is yesterday, the user is in danger of losing their streak.
+    let danger = top.toISODate() === today.minus({ days: 1 }).toISODate();
+
+    let streak = 1;
+    let running = true;
+    while (running && Object.keys(logs).length > 0) {
+        // Same general logic as `calculateStreak` in the frontend
+        // (max change of one day to continue streak)
+        const logKeys = Object.keys(logs).reverse();
+        for (const key of logKeys) {
+            const log = JSON.parse(AES.decrypt(logs[key].data, encryptionKey).toString(aesutf8));
+            if (top.day !== log.day || top.month !== log.month || top.year !== log.year) {
+                const logDT = DateTime.fromObject({ year: log.year, month: log.month, day: log.day });
+                if (logDT.toISODate() === top.minus({ days: 1 }).toISODate()) {
+                    top = logDT;
+                    ++streak;
+                } else {
+                    running = false;
+                    break;
+                }
+            }
+        }
+
+        // If the streak is going and we've run out of logs, try to fetch more
+        if (running) {
+            logs = await (await logRef.endBefore(Object.keys(logs)[0]).limitToLast(FETCH_LIMIT).get()).val();
+        }
+    }
+
+    res.send({ streak, danger });
+};
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