MongoDB vs PostgreSQL for SaaS

Q: When MongoDB Makes More Sense?

MongoDB's document model shines when: Deep nested documents — More than 3 levels of nesting without stable structure Extremely varied schemas — Each "user" has completely different fields (like a CMS) High write throughput — >100k writes/second to a single collection Your team knows MongoDB — Familiarity matters more than theoretical optimality

TL;DR

PostgreSQL wins for SaaS in 2026 for most use cases. JSONB gives you MongoDB-style flexibility when needed, the managed options are cheap (Neon free tier, Supabase free tier), and the type-safe ORM ecosystem (Prisma, Drizzle) is better for PostgreSQL. MongoDB makes sense for truly document-oriented data (unstructured content, nested arrays at depth), log storage, and teams who know MongoDB well.

When PostgreSQL Makes More Sense

SaaS data is inherently relational:

Users belong to organizations
Subscriptions belong to users
Feature flags apply to users or organizations
Audit logs reference users, resources, and actions

The relational model is natural here. PostgreSQL's JOINs, foreign keys, constraints, and transactions are features, not limitations.

When MongoDB Makes More Sense

MongoDB's document model shines when:

Deep nested documents — More than 3 levels of nesting without stable structure
Extremely varied schemas — Each "user" has completely different fields (like a CMS)
High write throughput — >100k writes/second to a single collection
Your team knows MongoDB — Familiarity matters more than theoretical optimality

Head-to-Head

Factor	PostgreSQL	MongoDB
Schema	Strict (migrations required)	Flexible
Relations	✅ Native JOINs	❌ Manual `$lookup`
Transactions	✅ ACID	✅ ACID (multi-doc since 4.0)
Full-text search	✅ tsvector	✅ Atlas Search
JSON storage	✅ JSONB	✅ Native
Type-safe ORM	Prisma, Drizzle (excellent)	Mongoose (good)
Managed services	Neon, Supabase, PlanetScale	MongoDB Atlas
Free tier	Neon 0.5GB free, Supabase 500MB	Atlas 512MB free
Serverless	Neon (serverless PG)	Atlas Serverless

PostgreSQL's JSONB: Best of Both Worlds

-- Store flexible data in PostgreSQL with JSONB
CREATE TABLE products (
  id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
  name TEXT NOT NULL,
  metadata JSONB,  -- Flexible! Different structure per row
  created_at TIMESTAMPTZ DEFAULT NOW()
);

-- Query JSON fields with full index support
CREATE INDEX ON products USING GIN(metadata);

SELECT * FROM products
WHERE metadata->>'category' = 'electronics'
AND (metadata->>'price')::numeric > 100;

JSONB in PostgreSQL is faster than MongoDB for read-heavy workloads and supports indexing into any JSON path.

Managed Hosting Comparison

For early-stage SaaS:

Service	Type	Free Tier	Production Cost
Neon	PostgreSQL	0.5GB free	$19/month
Supabase	PostgreSQL	500MB free	$25/month
PlanetScale	MySQL	5GB free	$39/month
MongoDB Atlas	MongoDB	512MB free	$57/month

PostgreSQL wins on cost at every tier.

Which Boilerplates Use Which

Boilerplate	Database
ShipFast	MongoDB (Mongoose) or PostgreSQL
T3 Stack	PostgreSQL (Prisma)
Supastarter	PostgreSQL (Supabase)
Makerkit	PostgreSQL (Supabase)
Epic Stack	SQLite → PostgreSQL
Open SaaS	PostgreSQL (Prisma via Wasp)
MERN Boilerplate	MongoDB

The trend is clear: new boilerplates default to PostgreSQL. MongoDB boilerplates are legacy or specifically for document-heavy use cases.

Find boilerplates by database type on StarterPick.