Firebase vs Supabase pricing: what you actually pay

Firebase charges for what you do: every document read, function call and gigabyte sent, with a free daily allowance and no base fee (Firebase pricing). Supabase charges for what you run: a plan from $25 a month plus a database instance per project, with generous included quotas and a spend cap: "The Pro Plan has a spend cap enabled by default to keep costs under control." (Supabase pricing).

So Firebase is usually cheaper for small or spiky apps and riskier when something runs away. Supabase is easier to predict and costs more at the start.

Supabase's free plan has one catch worth knowing: "Free projects are paused after 1 week of inactivity." Fine for a prototype, not for something people rely on.

Firebase has one paid plan, Blaze, with no monthly fee: you keep the free usage and pay per unit past it. Firestore in us-central1 costs $0.03 per 100,000 reads and $0.09 per 100,000 writes; Cloud Functions, $0.40 per million invocations past the first 2 million.

Supabase Pro starts at $25 a month and includes, per project, 8 GB of database disk, plus 100 GB of file storage, 250 GB of egress and 100,000 monthly active users. It also includes $10 a month of compute credits, enough for one Micro instance (1 GB of RAM). Past the included amounts: $0.125 per GB of disk, $0.0213 per GB of storage, $0.09 per GB of egress and $0.00325 per user. The next plan, Team, starts at $599 a month.

The part that surprises people is compute, which is per project. Supabase says it plainly: "Each project you launch increases your monthly Compute costs". A Small instance (2 GB of RAM) is $15 a month and a Large (8 GB, 2 vCPUs) $110, and the credits cover only one Micro. Three Small projects on Pro: $25 + $45 - $10 = $60 a month.

• Firebase counts operations. Every document read is billed, so the cost follows your traffic and your code. A query that reads 1,000 documents to show 10 costs 100 times more than it needs to, and nothing warns you.
• Supabase counts capacity. Queries aren't billed per row: you pay for the instance size. A heavy query makes the database slower, not the bill bigger, until you move to a larger instance.
• Both bill bandwidth. Egress past the included amount is billed on both, and it's the line that grows with downloads, images and video.

This is where they differ most. On Supabase Pro with the spend cap on, going over an included quota stops that usage: "further usage of that item is disallowed until the next billing cycle" (cost control). Your app may break, but the bill doesn't grow. The cap doesn't cover compute, read replicas, point-in-time recovery or other add-ons you choose.

Firebase has nothing like it for a whole project. A budget only sends alerts, often hours late (budget alerts), and a loop or an attack keeps billing until someone stops it. That's how the bills in our horror stories reached five figures.

• A small app or a side project: Firebase, often at $0. 1 million Firestore reads a day costs under $9 a month, while Supabase Pro is $25 before any usage. Supabase Free works too, as long as the project is used every week.
• Several small projects: Firebase gives every project its own free usage. On Supabase Pro each extra project adds compute, $10 a month at the smallest size.
• A steady, busy app: Supabase is easier to predict: a fixed instance and generous included quotas. On Firebase the bill follows reads and writes, so read-heavy screens are worth optimizing.
• Fear of a runaway bill: Supabase's spend cap is on by default. On Firebase you add the brake yourself: how to limit Firebase spending.

If you stay on Firebase, FireShield is that brake: alerts as soon as Google reports spend, spike detection on each service within minutes, and a Soft Kill or a Hard Kill when it matters.