Supabase vs Firebase: Picking a Backend for Your MVP

Supabase vs Firebase is really two decisions at once: a relational database you query with SQL against a document store you read one collection at a time, and a bill based on capacity against a bill based on every read and write. Supabase gives you Postgres, access rules inside the database and a predictable monthly floor. Firebase gives you Firestore, mobile SDKs with an offline cache, and costs that track how busy your app is.

This guide is for founders and small teams choosing a backend for a first product, and for anyone whose AI-built prototype already sits on one of them. It covers the data model, pricing with worked numbers, access rules, mobile support and what each platform commits you to. If the rest of the stack is still open, our guide to choosing a tech stack for an MVP covers the decisions that sit around this one.

Key takeaways

• Supabase charges for capacity. The Pro plan starts at $25 a month, includes $10 of compute credits, and places no limit on the number of API requests.
• Firebase charges for activity. Firestore costs $0.03 per 100,000 document reads and $0.09 per 100,000 writes in Iowa (us-central1), with no subscription fee on the pay-as-you-go plan.
• Pick Postgres when records relate to each other and you will want joins, reports and constraints. Pick Firestore when you are shipping a mobile app that has to keep working offline.
• Access rules live in different places: row level security inside Postgres, Security Rules in front of the Firestore API. Firestore rules that read other documents add billed reads.
• Firebase is no longer document-only. SQL Connect, previously called Data Connect, runs a managed Cloud SQL for PostgreSQL database behind a GraphQL API.

Supabase vs Firebase: the short version

Both platforms hand you a database, authentication, file storage, serverless functions and hosting behind one SDK, and both are good enough to launch a real product on. The differences that matter are the shape of your data, where authorisation runs, and how the invoice is calculated.

Read the billing row twice. It is the line founders feel in month three, and it is the hardest one to change afterwards.

How do the two data models differ?

Supabase is Postgres, so data sits in tables with types, foreign keys and constraints, and you query across them with SQL. Firestore stores JSON-like documents inside collections, and a single query reads from one collection or one collection group.

When tables and SQL win

Anything with relationships. Invoices belong to customers, customers belong to organisations, and one SQL statement can answer "revenue per organisation this month". In Firestore the same answer is several reads stitched together in your own code, or a counter you maintain on every write and hope never drifts.

The surrounding tooling matters as much as the query language. Constraints stop bad data at the door, migrations are versioned files, and every analytics, billing and reporting tool already speaks SQL. Our comparison of relational and document databases for early products goes deeper into the modelling trade-off itself.

When documents win

Firestore is strongest where the unit of work is a document and the client is a phone. The SDK caches data on the device, keeps working with no connection and syncs when one returns. That is weeks of engineering you would otherwise write yourself, and it is the single best reason to choose Firebase.

The constraints appear as queries get more specific. Combining an equality filter with an inequality filter needs a composite index, OR queries are capped at 30 disjunctions, and not-in accepts at most 10 values, as Firestore's documentation on simple and compound queries sets out. None of that blocks a product. It does mean the data is modelled around the screens you plan to show, so changing those screens later can mean reshaping the data behind them.

How much does Supabase or Firebase cost?

At small scale both are close to free, so the real question is which meter your app spins fastest. Supabase sells capacity: compute, disk, egress and monthly active users. Firebase sells operations: document reads, writes, deletes and function invocations.

Those figures come from the Supabase pricing page, the Firebase plan comparison and Google Cloud's Firestore pricing for us-central1, read in October 2026. All three change often enough to check before you subscribe.

What a working app actually pays

Take a feed screen that reads 50 documents every time someone opens it, with 20,000 visits a month. That is one million reads, which costs $0.30 on Firestore. Grow to 100 million reads a month and the same line is $30. A million writes adds $0.90.

The same product on Supabase pays $25 whether it serves a thousand requests or ten million, because requests are not metered. Move from the included Micro instance to Small and compute goes from $10 to $15, so the bill lands near $30 a month.

The pattern is consistent. A chatty app with modest data usually ends up cheaper on Supabase, because reads are free and compute is flat. A quiet app with a handful of users is usually cheaper on Firebase, because almost no traffic means almost no bill.

Where each bill surprises people

• Firestore bills a minimum of one document read per query, even a query returning nothing, and an offset charges a read for every document it skips.
• Security Rules that call get() or exists() are billed for the documents they read to reach a decision.
• Realtime listeners keep charging. Each updated document in the result set is a read, and with offline persistence on, a listener disconnected for more than 30 minutes is billed like a brand-new query when it reconnects.
• Supabase has a floor, not a ceiling. The subscription plus hourly compute arrives whether anyone used the product that month, and preview branches bill by the hour until somebody deletes them.
• Supabase keeps a spend cap on by default on Pro, which stops usage past the included quota instead of billing for it. That protects the invoice and accepts the outage, so decide deliberately which you want.

Compute sizes, connection limits and the point where a bigger instance is genuinely the answer are covered in our notes on what breaks first as Supabase traffic grows.

How do access rules compare?

Both platforms expose the database to the browser or the app, so both put an authorisation layer in between. The difference is where the rule runs and what it costs to evaluate.

On Supabase a policy is part of the query plan. Postgres appends it to every statement against the table, and nothing that reaches the table escapes it:

alter table public.invoices enable row level security;

create policy "Owners read their own invoices"
on public.invoices for select
to authenticated
using ((select auth.uid()) = owner_id);

On Firestore the same intent lives in a rules file deployed alongside the app:

match /invoices/{invoiceId} {
  allow read: if request.auth != null
              && request.auth.uid == resource.data.ownerId;
}

Two practical differences follow. Firestore's rules govern the mobile and web client libraries, while server code using the Admin SDK runs with privileged access, so a backend job can quietly ignore them. And a Firestore rule that reads another document to decide, which is how most team and role checks are written, adds reads to the bill on every request.

Both are easy to leave half-finished, and neither shows a warning on screen when they are. The fastest check is to create a second account and try to reach the first account's data, then try again logged out. Our walkthrough of the tables a generated app usually leaves unprotected covers the policies to write for owner, team and admin rows.

Which should you pick for your MVP?

Pick on the shape of the product first and the price second, because at MVP volumes the difference between the two bills is usually smaller than one week of rework.

One more input: what your tools already generate. Most AI app builders scaffold Supabase projects by default, so a prototype that exists is a reason to stay unless the data model is genuinely wrong for the product.

What are you committing to?

Supabase is Postgres with services around it. Leaving means a dump and restore plus replacing Auth, Storage and the data API, which is real work but a known migration, and the database half of it is a standard export.

Firestore has no equivalent to restore into. Moving means reshaping documents for whatever comes next and rewriting the queries, the rules and the client code that depended on them. That is not an argument against choosing it, only against choosing it for a product whose data model you expect to question in a year.

Firebase has narrowed the gap. Firebase SQL Connect runs a fully managed Cloud SQL for PostgreSQL database with a GraphQL API, type-safe SDKs for web, Android, iOS and Flutter, and integration with Firebase Authentication. If you want Google's platform with a relational database underneath, that is now a supported path rather than a workaround.

Common mistakes

• Choosing on the free tier. Both free tiers are generous and neither resembles the plan you will be on six months later.
• Modelling Firestore like a relational database. Collections of tiny documents that always get fetched together turn one screen into hundreds of billed reads.
• Assuming Postgres means no realtime. Supabase streams database changes, and Firebase has no monopoly on live updates.
• Leaving access rules until after launch. On both platforms the API is public from the first deploy, not from the first paying customer.
• Running development and production in one project. Two environments cost very little on either platform and save one bad afternoon.

Frequently asked questions

Is Supabase cheaper than Firebase?

It depends on whether your app is busy or idle. Supabase has a fixed floor of $25 a month on Pro with unmetered API requests, so heavy read traffic costs nothing extra. Firebase has no floor but charges per operation, so a quiet app is cheaper and a read-heavy one eventually is not.

Can I use Firebase Authentication with a SQL database?

Yes. Firebase SQL Connect is built on Cloud SQL for PostgreSQL and supports end-user authentication through Firebase Authentication, so you can keep Google's sign-in and still store relational data. It is a different product from Firestore, with its own pricing and its own SDKs.

Which is better for a mobile app?

Firebase, if offline behaviour matters. Its native SDKs cache data on the device and resolve syncing when connectivity returns, and reproducing that on another backend is a project in itself. For a mobile app that is mostly online and talks to an API, either platform is fine.

Can I move from Firebase to Supabase later?

You can, and it is a rewrite of the data layer rather than a download. Documents have to be mapped into tables, rules become policies, and every client query is written again against SQL. Plan it as a project with its own timeline, not a weekend migration.

Picking a backend you will not have to redo

Match the platform to the product: Postgres on Supabase when records relate to each other and you will want to report on them, Firestore when an offline-capable mobile client is the point. Check the pricing pages for the numbers above, work out which meter your app spins fastest, and set a spend cap before launch day rather than after it.

Whichever you choose, the launch-blocking work is the same: access rules, payments, environments and backups. If you would rather hand that to senior engineers on a fixed price, with a working demo every week, see how we approach backend and API engineering.