Strip away the feature tables and the choice is one decision: a proprietary NoSQL document store, or Postgres. Firebase gives you Firestore, real-time sync that is genuinely excellent, and a billing model that charges per document read. Supabase gives you a standard Postgres database with SQL, joins, and constraints, plus auth and storage wrapped around it. Everything else follows from that, including how hard it is to leave.
Both are good products, and most comparisons list identical features on both sides without saying what actually differs. What differs is the data model, and the data model decides the shape of your application code for years.
Table of contents
- The data model, which is the whole decision
- Real-time
- Pricing shapes, and which one surprises you
- Auth, storage, and functions
- Lock-in and the exit path
- A reasonable way to choose
- How this fits the rest of the stack
- FAQ
The data model, which is the whole decision
Firestore stores documents in collections. There are no joins. Data you display together should be stored together, so you denormalise — the same customer name is copied into every order document, and when the customer renames themselves you update every copy.
Supabase is Postgres. You get foreign keys, joins, transactions, views, window functions, and constraints that make invalid states unrepresentable rather than merely discouraged.
-- Postgres: the join is free and the constraint is real
SELECT o.id, o.total, c.name
FROM orders o
JOIN customers c ON c.id = o.customer_id
WHERE o.created_at > now() - interval '7 days';// Firestore: fetch orders, then fetch each customer, then stitch
const orders = await getDocs(query(
collection(db, 'orders'),
where('createdAt', '>', sevenDaysAgo)
));
// N+1 unless you denormalised customerName into the order at write timeNeither is wrong. Document stores fit hierarchical data with predictable access patterns; relational databases fit data that gets queried in ways you did not anticipate. The honest question is: do you know all your queries in advance? For most products the answer is no, which is a point for Postgres.
Real-time
Firebase’s real-time sync is its strongest feature and has been for a decade. Listeners fire on change, the client library handles offline queues and reconnection, and edits made offline sync when the device comes back. For a collaborative or mobile-first app that is difficult to match.
Supabase does real-time too, over Postgres logical replication, and it works well for change subscriptions. What it does not give you out of the box is Firebase’s offline-first persistence and conflict handling on mobile.
- Building chat, presence, collaborative editing, or an offline-capable mobile app — Firebase’s real-time is a genuine advantage.
- Building a dashboard, a SaaS product, or anything with reporting — the advantage is smaller than it sounds, and SQL matters more.
Pricing shapes, and which one surprises you
This is where the two differ in kind rather than degree.
Firebase charges per operation: document reads, writes, deletes, plus storage and bandwidth. A dashboard that reads 500 documents on load, viewed by 200 users 20 times a day, is two million reads a day. The bill scales with usage patterns rather than data size, and an accidental listener in a useEffect without a cleanup can cost real money overnight.
Supabase charges for the instance: compute, storage, bandwidth. A query that reads a million rows costs the same as one reading ten — it just takes longer. That is far easier to forecast, and the failure mode is a slow query rather than an invoice.
Neither is universally cheaper. Firebase is often cheaper at very low traffic, where a small instance still bills at a floor. Firebase gets expensive faster when read patterns are heavy, and it is harder to predict, which for a small team is a cost in itself.
Auth, storage, and functions
Both cover the same ground here and the differences are matters of taste.
- Auth — both do email and password, magic links, OAuth providers, and JWTs. Firebase has broader provider coverage and better mobile SDKs. Supabase stores users in a Postgres table you can join against, which is quietly a big deal.
- Storage — both do object storage with access rules. Comparable.
- Functions — Firebase Cloud Functions are mature with a large ecosystem. Supabase Edge Functions run on Deno at the edge, are faster to start, and have a smaller ecosystem.
- Row-level security — Supabase leans on Postgres RLS, so access rules are SQL policies. Firebase uses its own security rules language. RLS is harder to learn and far more expressive.
That auth point deserves emphasis. In Supabase, auth.users is a table, so JOIN between a user and their data is ordinary SQL. In Firebase, the auth system is separate from Firestore and you keep a parallel user document in sync by hand.
Lock-in and the exit path
The asymmetry here is the strongest practical argument, and it is the one most comparisons skip.
Supabase is Postgres with open-source services around it. Leaving means pg_dump and restoring into any Postgres anywhere. Your SQL is portable, your schema is portable, and self-hosting is a documented path rather than a theoretical one.
Firestore is proprietary. There is no other implementation. Leaving means exporting documents to JSON, designing a relational schema, writing migration code, and rewriting every query in your application — because the query patterns were shaped by the absence of joins.
Teams migrate off Firebase reasonably often, usually driven by cost at scale or the need for reporting queries that Firestore cannot express. It is a project measured in weeks, not an afternoon. That risk is worth pricing at the start, when it costs nothing to avoid.
A reasonable way to choose
- Firebase — mobile-first, offline support matters, real-time collaboration is core, the access patterns are known and hierarchical, and you want to ship this week.
- Supabase — you want SQL, you expect reporting and analytics, the schema will evolve, you value the exit path, or your team already knows Postgres.
- Neither — the app is mostly a normal web application with a normal database. A managed Postgres and a backend service you control is less magic and fewer surprises.
That third option gets dismissed too quickly. A backend-as-a-service earns its keep when it removes work you would otherwise do. When the app is a web service talking to a relational database, the BaaS layer is mostly adding a vendor between you and Postgres.
That is the shape RunxBuild handles directly: a managed MySQL or Postgres instance with connection limits, backups, and private networking, next to a Node, Python, Go, Ruby, Java, or Docker service deployed from your GitHub repository. The database is a normal one, so your SQL and your migration tooling are whatever you already use, and moving is pg_dump rather than a rewrite.
How this fits the rest of the stack
Pick Firebase for offline-capable, real-time, mobile-first products with predictable access patterns. Pick Supabase when you want SQL, evolving schemas, and a migration path that does not involve rewriting your queries. Price the exit while it is still free to do so — that asymmetry is the most durable difference between them.
And consider whether you need the layer at all. A service plus a managed Postgres is a smaller surface with fewer billing surprises. If you are comparing what that costs, the RunxBuild hosting calculator shows the service, the database, the storage, and the bandwidth as separate line items so you can see which part actually drives the number.
Useful related references:
FAQ
What is the main difference between Firebase and Supabase?
The database. Firebase uses Firestore, a proprietary NoSQL document store with no joins, so you denormalise data. Supabase is managed Postgres, so you get SQL, joins, foreign keys, and transactions. Every other difference — query patterns, reporting, migration difficulty — follows from that one.
Is Supabase cheaper than Firebase?
It depends on your read patterns rather than your scale. Firebase bills per document read and write, so a read-heavy dashboard can get expensive quickly and unpredictably. Supabase bills for the instance, so a heavy query costs time rather than money. Firebase is often cheaper at very low traffic; Supabase is easier to forecast.
Can I migrate from Firebase to Supabase?
Yes, but it is a real project. You export Firestore documents to JSON, design a relational schema, and rewrite queries that were built around the absence of joins. Teams typically measure it in weeks. Migration in the other direction, or off Supabase entirely, is much simpler because it is a standard Postgres dump.
Does Supabase have real-time like Firebase?
It has real-time subscriptions built on Postgres logical replication, which handles change notifications well. What it does not match is Firebase’s offline-first client persistence and conflict resolution on mobile, which is Firebase’s strongest single feature and the main reason to choose it.
Do I need Firebase or Supabase at all?
Not necessarily. If your app is a web service talking to a relational database, a managed Postgres or MySQL instance plus a backend service you deploy from your repository covers the same ground with fewer moving parts. A backend-as-a-service earns its place mainly when the real-time or mobile SDK work is genuinely saving you time.