The backend choice for a new app is one of the decisions that's genuinely hard to reverse later, because so much application logic ends up shaped around it. Here's how the three common paths compare.

Speed to launch

Firebase and Supabase both get you moving fast — authentication, a database, and hosting are ready out of the box, so early development is mostly application logic rather than infrastructure. A fully custom backend is slower to get to a first working version, since you're building the foundational pieces yourself, but that investment pays off as requirements grow more specific.

Cost at scale

At meaningful scale, the two platforms diverge significantly: for a workload around 10,000 daily active users, Supabase's usage-based Postgres pricing tends to land in the tens to low hundreds of dollars a month, while Firebase's per-read Firestore billing can run into the high hundreds to low thousands for comparable usage. A custom backend has its own hosting costs, but without the platform margin — the tradeoff is you're also responsible for the infrastructure work the platform would otherwise handle.

Vendor lock-in

This is where the platforms differ most. Firebase's Firestore is a proprietary NoSQL structure, queried through Firebase-specific SDKs and secured with a Firebase-specific rules language — migrating away later means rebuilding a meaningful part of your data layer. Supabase is built on standard PostgreSQL; because the data lives in an open, standard format, migrating to another Postgres host is comparatively straightforward, and self-hosting is possible since Supabase is open source. A custom backend has no platform lock-in by definition, at the cost of owning everything yourself.

Data ownership and query flexibility

Firestore's document structure is fast for simple lookups but limited for complex relational queries — joining and filtering across collections is more awkward than in a relational database. Supabase gives you full SQL over a real relational database, which suits apps with more complex data relationships. A custom backend can use whichever database model actually fits your data, since nothing is dictated by the platform.

Comparison summary

Which fits which project

Firebase suits apps that prioritise speed of development and offline-first mobile sync over relational query needs. Supabase suits most new web and mobile projects wanting relational data, predictable pricing, and low lock-in without building infrastructure from scratch. A custom backend suits apps with requirements specific enough — scale, compliance, unusual data relationships — that a general-purpose platform becomes a constraint rather than a help.

We choose the backend based on the specific project's requirements rather than defaulting to one platform — the right answer genuinely differs between a fast-moving MVP and a compliance-heavy enterprise system.