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It's a split decision.
Choose MongoDB when your application is built around document data and you want Atlas services alongside the database, including search and vector search. Choose PostgreSQL when you want an open-source object-relational database that your team can self-host and operate. MongoDB offers a free Atlas tier, but production clusters have published hourly prices. PostgreSQL has no software charge, but hosting and operational costs depend on how you run it.
01Side by side
| MongoDB | PostgreSQL | |
|---|---|---|
| Pricing model | Atlas bills hourly; dedicated starts at $56.94/month. | Open-source software; no paid database plan. |
| Free tier | M0: 512 MB, 32 MB sort memory, up to 100 ops/sec. | Free software; no published seat or usage limits. |
| Open source and licence | Enterprise Advanced includes a commercial licence. | Open source under the OSI-approved PostgreSQL Licence. |
| Self-hosting | Self-managed software is available. | Self-hostable open-source database. |
| Data model and API | Document model with a single query API. | Open-source object-relational database system. |
| Documentation and community | Documentation, forums, University, and community resources. | Official documentation and community resources. |
| Integrations | MongoDB says it integrates with 100+ technologies. | Homepage does not list specific integrations. |
| Deployment model | Atlas across clouds or self-managed infrastructure. | Self-managed open-source software. |
MongoDB Choose MongoDB if
- Choose MongoDB if your application centers on document data.
- Choose MongoDB if you want Atlas-managed database and search services.
- Choose MongoDB if its listed M0 or paid cluster tiers fit your workload.
PostgreSQL Choose PostgreSQL if
- Choose PostgreSQL if open-source licensing is a requirement.
- Choose PostgreSQL if your team wants to manage its own database hosting.
- Choose PostgreSQL if you want software with no database licence charge.
02Pricing at real usage
MongoDB Atlas M0 is free forever and includes 512 MB of storage, 32 MB of sort memory, and up to 100 operations per second. Atlas Flex lists a $0.011/hour base rate, 5 GB of storage, and usage costs of $8–$30/month. Dedicated clusters start at $56.94/month; listed hourly rates range from $0.08 for M10 to $33.26 for M700. Atlas bills clusters hourly with monthly invoices, and the pricing page lists no annual billing option.
PostgreSQL is free-of-charge open-source software, with no published seat or usage limits. That is the database licence cost, not the cost of running a production service: teams supply hosting and operations, so infrastructure spend depends on deployment and workload. PostgreSQL has no paid database plans listed. Compare total hosting, support, and operational costs rather than treating the software price as the full bill.
03API, SDKs and integration
MongoDB describes a flexible document model and a single query API for application data. Atlas adds database search, vector search, analytics, and stream-processing capabilities. Its homepage points developers to documentation, community forums, and MongoDB University, and says the product integrates with more than 100 technologies.
PostgreSQL is an object-relational database system. Its homepage directs developers to official documentation and community resources for installing, using, and learning the system. Neither homepage specifies SDK languages or a CLI, so check the documentation for the drivers and command-line tools that match your application stack. PostgreSQL's homepage does not list named integrations; assess specific extensions and external tools against the version and hosting service you plan to use. The available descriptions do not establish a like-for-like SDK or protocol comparison.
04Open source, self-hosting and lock-in
PostgreSQL is open-source software under the OSI-approved PostgreSQL License and can be self-hosted. Your team supplies the hosting and operational work. MongoDB offers Atlas as a cloud service and self-managed software for your infrastructure. Enterprise Advanced includes a commercial licence; its licence terms and pricing should be checked for the deployment you plan.
MongoDB's homepage lists Relational Migrator as a tool for migrating to MongoDB, but does not describe general-purpose export formats or a reverse migration path. Confirm how you will extract data and move application workloads before relying on Atlas-specific services. Moving between a document model and an object-relational database can also require changes to data structures and application code. Treat migration effort as a project-specific question, not a guarantee based on the database licence or deployment option.
Questions people ask
What is the main difference between MongoDB and PostgreSQL?
MongoDB is a document-model database with a single query API and cloud or self-managed deployment options. PostgreSQL is an open-source object-relational database system. The practical choice starts with how your application represents data and whether you want a managed Atlas deployment or to operate the database yourself.
Is MongoDB or PostgreSQL cheaper?
PostgreSQL has no database software charge, but self-hosting still requires infrastructure and operational work. MongoDB Atlas has a free M0 tier, then paid options including Flex usage costs of $8–$30/month and Dedicated clusters starting at $56.94/month. Compare the full hosting and support bill for your workload.
Can I self-host MongoDB and PostgreSQL?
Yes. MongoDB offers self-managed software for your own infrastructure as well as Atlas. PostgreSQL is open-source software that teams can self-host. In either case, plan for the work of provisioning, operating, and maintaining your deployment; the product choice alone does not determine that effort.
Which database should I choose for an application?
Choose MongoDB if a document model and Atlas services such as search or vector search match your design. Choose PostgreSQL if you want an open-source object-relational system and are prepared to supply hosting and operations. Compare data-model fit, deployment requirements, and total running costs before committing.