Which is cheapest — Firebase, Supabase, or MongoDB Atlas?

All three have free tiers: Firebase Spark (free) includes 1 Firestore GB, Supabase free includes 500MB PostgreSQL, MongoDB Atlas M0 includes 512MB. First paid tier: Supabase Pro at $25/month is cheapest. Firebase Blaze is pay-as-you-go (starts at $0, scales with usage). MongoDB M2 is $57/month. For predictable costs on a small project, Supabase Pro at $25/month is most affordable.

When should I choose Supabase over Firebase?

Choose Supabase when: you prefer SQL/PostgreSQL over NoSQL, you want open-source with no vendor lock-in, you need row-level security, or you're building with Next.js/React. Choose Firebase when: you need real-time sync for mobile apps, you're in the Google ecosystem, or you want Google's scale guarantees. Supabase is generally 40–60% cheaper than Firebase at mid-scale usage.

Is Firebase free for small projects?

Yes. Firebase Spark plan is free with no time limit: includes 1GB Firestore storage, 50K document reads/day, 20K writes/day, 5GB Firebase Storage, 10GB bandwidth/month, and Google Authentication. The free tier is generous enough for prototypes and small production apps. When you exceed limits, you must upgrade to the pay-as-you-go Blaze plan.

MongoDB Atlas vs Supabase — which is better for startups?

Supabase is better for startups that: want PostgreSQL's relational model, prefer open-source with self-hosting option, or need built-in auth and storage. MongoDB Atlas is better when: you need flexible document storage (variable schemas), you're coming from a MongoDB background, or you need Atlas Search. For new projects, Supabase at $25/month vs MongoDB M2 at $57/month gives Supabase a significant cost advantage.

Firebase vs Supabase vs MongoDB Atlas — Backend Pricing Comparison 2026

Quick Price Comparison

Feature	Firebase	Supabase	MongoDB Atlas
Free Tier Storage	1 GB Firestore	500 MB	512 MB
Paid Tier Minimum	Pay-as-you-go	$25/month	$57/month
Database Type	Real-time JSON	PostgreSQL (SQL)	NoSQL (BSON)
Included Auth?	✓	✓	✗
Real-Time Subscriptions?	✓ Native	✓ Native	△ Via Change Streams

Detailed Cost Breakdown by Scenario

Scenario 1: Hobby Project (Small Storage, Low Traffic)

Estimated 1,000 reads/day, 100 writes/day, 500 MB storage

Firebase ~$0–$5/month

• 30K reads (0.3M) = $0.18
• 3K writes (30K) = $0.05
• 500 MB storage (free tier)

Supabase $25/month

• Pro plan minimum
• No usage overage

MongoDB $57/month

• Shared M2 minimum
• No usage overage

Scenario 2: Growing Startup (1 Million reads/month, 100K writes/month)

Firebase ~$35–$45/month

• 1M reads = $6.00
• 100K writes = $1.80
• 5 GB storage overage = $0.90
• Auth users (100K) = free (first 1M free)

Supabase $25–$75/month

• Pro plan = $25/month
• Auth users (100K) = free
• Overage storage (5 GB) = $1.25
• Potential edge function costs = ~$10–20/month

MongoDB $57–$95/month

• Shared M2 ($57) or M5 ($95)
• Storage included (2–10 GB)
• No per-operation charges

Scenario 3: Large Production App (50M reads/month, 5M writes/month)

Firebase ~$300–$400/month

• 50M reads = $300
• 5M writes = $90
• 50 GB storage = $9
• Cloud Functions calls (10M) = $4

Supabase $75–$150/month

• Team plan = $599/month (or Pro $25)
• Storage overage (40 GB) = $10
• Edge function costs could vary
• Much cheaper at high volume vs Firebase!

MongoDB $150–$300/month

• Dedicated M20 = $190/month
• Storage overage (10 GB) = $1
• Backup storage (50 GB) = $10
• Consistent, predictable costs

Feature Comparison Matrix

Feature	Firebase	Supabase	MongoDB Atlas
Data Type	Real-time JSON	Relational (SQL)	Document (NoSQL)
Query Language	JavaScript API	SQL/PostgreSQL	MongoDB Query Language
Real-Time Subscriptions	✓ Excellent	✓ Good (Postgres Notify)	△ Change Streams (slower)
Authentication	✓ Built-in (Google, GitHub, email)	✓ Built-in (Supabase Auth)	✗ Requires 3rd party
Hosting	✓ Cloud Run + CDN	✓ Vercel/Supabase	✗ Database only
Serverless Functions	✓ Cloud Functions	✓ Edge Functions	✗ Requires AWS/others
Offline Support	✓ Native (Realtime DB)	△ Requires 3rd party	✗ No
Flexible Schema	✓ JSON (very flexible)	△ Can be done (JSONB)	✓ Schema-less
Complex Queries	✗ Limited	✓ Full SQL power	✓ Good aggregations
Transactions	△ Basic	✓ Full ACID	✓ Full ACID (4.0+)

When to Choose Each

Choose Firebase when:

Building real-time apps (chat, collaborative editing, notifications)
You want the fastest time-to-market (auth, hosting, functions included)
Your data is under 1 TB and queries are simple
You need offline-first mobile apps with sync
Budget is tight for hobby projects (<$10/month)

Choose Supabase when:

You need relational data with complex queries (SQL)
You want open-source flexibility and self-hosting option
You need Row-Level Security (RLS) for multi-tenant apps
You want to avoid vendor lock-in
Scale is high (50M+ operations/month) and budget matters

Choose MongoDB Atlas when:

You have semi-structured or evolving data (loose schema)
You want predictable, flat billing (no per-operation charges)
You're building at scale with DevOps expertise
You want to avoid SQL and embrace document-oriented design
You need multi-region replication or advanced cluster features

Pricing Trends & Hidden Costs

Firebase: Looks cheap at first, but operations costs compound quickly. Hidden costs: Cloud Functions ($0.40/M invocations), bandwidth charges, free tier changes.

Supabase: Fixed monthly cost is predictable. Storage overage ($0.25/GB) can add up if you store large files. Team plan ($599/month) is expensive jump from Pro ($25).

MongoDB: Cluster costs are hourly but consistent. No surprise per-operation charges. Backup storage ($0.20/GB) is the main hidden cost. Dedicated clusters more expensive than shared.

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