Database & Backend Platform · decision tool

Firebase vs MongoDB Atlas — for your app, not in general

Firebase's realtime BaaS or MongoDB Atlas's document database? Set your users, data size and constraints; the verdict, monthly cost and risks update live from verified pricing.

Prices verified 2026-07-15 against official pricing pages · fit weights are our estimates (see methodology) · share the URL to share your configuration

As of Jul 2026, with 5,000 monthly active users, 5 GB database size, 40 GB monthly egress, 1,000 db operations per user / month, 24 compute active hours / day, a $50 budget for this slot, Firebase (Firestore) ranks first for these inputs at 89% fit and a StackSays-estimated $7.30/month (MongoDB Atlas: 80% fit, $8.00/month). Fit weights are our estimates; prices trace to official pages. Change any input below and the verdict recomputes.

Your situation

The verdict updates as you move these.

Monthly active userspeople actually hitting the app each monthDatabase size (GB)rows + indexes; a typical early SaaS is 1–10GBMonthly egress (GB)data served out of the DB/API to clientsDB operations per user / month≈100 light · 1,000 normal · 10,000 heavy — only per-operation DBs (Firestore) bill thisBudget for this slot ($/mo)what you'd accept paying for the database layerTeam size1 = solo; bundled platforms save glue time for small teams

Clear pick for your inputs

Firebase (Firestore)fit 89% · est $7.30/mo

Google's document database with realtime sync and a huge mobile ecosystem

vs MongoDB Atlas: fit 89% against 80%, est $7.30 against $8.00–$30.00 per month

Firebase (Firestore)fit 89%

$7.30/mo

MongoDB Atlasfit 80%

$8.00–$30.00/mo

Comparing 2 tools head-to-head. Open the full field (7 options) →

The decision, in plain words

For a solo builder at 5,000 monthly active users and a $50.00/mo budget for the database slot, Firebase (Firestore) leads at 89% fit and $7.30/mo. The two rules doing the work: budget fit (~$7.3/mo is 15% of your $50/mo budget); batteries included (Bundles auth, file storage, realtime — fewer services to glue at team size 1).

The gap to MongoDB Atlas (80% fit) is wide at these inputs — you'd need to change your requirements, not your taste, to flip it.

Honest weak spot of the pick: proprietary data model — leaving means rewriting the data layer.

Generated from the calculation above — every number traces to the sourced data; nothing here is written by an AI making things up.

Why Firebase (Firestore) scores 89%

Budget fit (weight 30, our estimate) — ~$7.3/mo is 15% of your $50/mo budget+30

Batteries included (weight 12, our estimate) — Bundles auth, file storage, realtime — fewer services to glue at team size 1+12

Exit cost (weight 4, our estimate) — Proprietary data model — leaving means rewriting the data layer-4

Ecosystem maturity (weight 8, our estimate) — established — our estimate from ecosystem age, docs and hiring pool+8

Free-tier runway (weight 10, our estimate) — Free tier exists (1GiB Firestore, 50K reads / 20K writes / 20K deletes per day, 50K auth MAU, 10GiB egress) — a cheap staging/dev lane even after you outgrow it+4

Total (lines sum exactly)50

Possible range −64…+64 (sum of active rule weights) · fit % = (total + max) / (2 × max)(50 + 64) / 128 = 89%

How the $7.30/mo estimate is calculated

Database storage overage — 4GB over 1GB included × $0.18/GB$0.72

Egress overage — 29.2GB over 10.8GB included × $0.15/GB$4.38

Document reads overage — 2.48M over 1.52M included × $0.6/M$1.49

Document writes overage — 0.39M over 0.608M included × $1.8/M$0.71

Note — Firestore nam5 rates: $0.06/100K reads, $0.18/100K writes, $0.18/GiB storage; deletes ($0.02/100K) not modeled. Ops derived from your per-user activity input (80/20 read/write split, our estimate)$0

Monthly total (lines sum exactly)$7.30

What could change this verdict

Cost risk

Estimated now (StackSays estimate, not your final bill)$7.30/mo · Blaze (pay-as-you-go)

Free-tier statusFree tier exceeded (database storage 5GB > 1GB cap)

Biggest unpriced/uncertain variableFirestore nam5 rates: $0.06/100K reads, $0.18/100K writes, $0.18/GiB storage; deletes ($0.02/100K) not modeled. Ops derived from your per-user activity input (80/20 read/write split, our estimate)

Official prices verified 2026-07-15; calculation is deterministic code over those prices.

At a glance

Tool	Free tier	Paid entry	Verified
Firebase (Firestore)	1GiB Firestore, 50K reads / 20K writes / 20K deletes per day, 50K auth MAU, 10GiB egress	Pay-as-you-go — Firestore nam5 rates: $0.06/100K reads, $0.18/100K writes, $0.18/GiB storage; deletes ($0.02/100K) not modeled. Ops derived from your per-user activity input (80/20 read/write split, our estimate)	2026-07-15
MongoDB Atlas	512MB storage, shared CPU/RAM, ~100 ops/sec cap	Flex tier $8/mo	2026-07-15

Where did you land?anonymous, one click

Data sources

Tool	Source	Verified
Firebase (Firestore)	Firebase pricing page	2026-07-15
MongoDB Atlas	MongoDB Atlas pricing page	2026-07-15

A monitor re-checks these pages for changes; when a vendor moves a price, the date updates and every verdict recomputes.

Keep deciding