What database should I use for a SaaS app with users and billing?

For most SaaS apps with users and billing, the best default choice is PostgreSQL.

Why PostgreSQL is usually the best fit

• Great for relational data: users, subscriptions, invoices, payments, organizations, roles, etc.
• Strong consistency: important for billing and access control.
• Flexible: handles structured data well and can also store JSON when needed.
• Mature ecosystem: works well with ORMs, migrations, background jobs, and analytics tools.
• Easy to scale initially: plenty fast for a startup to mid-size SaaS.

Typical SaaS data model in Postgres

• users
• organizations / accounts
• memberships
• plans
• subscriptions
• invoices
• payments
• audit_logs

Common stack choice

• PostgreSQL as the main database
• Redis for caching, sessions, rate limiting, and job queues
• Optional:
  • Object storage (S3, etc.) for files
  • Analytics DB later if reporting gets heavy

When you might choose something else

• MySQL: also fine, especially if your team already knows it well
• MongoDB: usually not ideal as the primary DB for billing-heavy SaaS
• DynamoDB / NoSQL: useful for very specific high-scale access patterns, but usually overkill early on
• SQLite: good for prototypes, not ideal for multi-user production billing apps

Important billing advice

Billing data should be treated carefully:

• Use transactions
• Keep an immutable payments/invoices ledger
• Don’t rely only on Stripe/webhook state without reconciliation
• Store provider IDs and event IDs for idempotency

Practical recommendation

If you’re starting a SaaS today:

1. Use PostgreSQL
2. Use Stripe for billing
3. Add Redis if/when you need caching or background jobs

If you want, I can also suggest a full SaaS stack (database, auth, billing, queue, hosting) based on your app size and language/framework.