Choose DynamoDB if you build on AWS and want a serverless key-value and document database with no versions to upgrade, no maintenance windows and capacity that can scale down to zero. Choose MongoDB if you want a rich document database you can self-manage anywhere or run on MongoDB Atlas, with ad hoc queries, indexing and real-time aggregation. Both have a free way in: DynamoDB's free tier includes 25 GB of storage each month, and MongoDB Atlas has a Free tier with 512MB for learning.
I read Amazon's DynamoDB product page, developer guide and free tier page, and MongoDB's what is MongoDB page, documentation, licensing page and Atlas plans page, to compare how each is built and sold.
DynamoDB and MongoDB at a glance
| Amazon DynamoDB | MongoDB | |
|---|---|---|
| Data model | Key-value and document | Flexible JSON-like documents |
| Where it runs | AWS only, fully managed | MongoDB Atlas cloud or self-managed |
| Upgrades | No versions and no maintenance windows | Versioned releases, with MongoDB 9.0 announced |
| Scaling | On-demand mode scales to zero, or provisioned capacity | Replication and native sharding built in |
| Licence | AWS service terms | SSPL v1 for the server, Apache 2.0 for drivers, commercial licences available |
| Free option (as of October 2026) | Free tier: 25 GB storage, 25 read and 25 write capacity units a month | Atlas Free with 512MB, plus self-managed Community Edition |
DynamoDB has no versions to upgrade
This is the detail I didn't expect. Amazon's developer guide says DynamoDB has no versions at all, major, minor or patch, and no maintenance windows, with zero downtime maintenance. You don't provision servers or patch software. Its on-demand mode bills per request and scales tables up or down instantly, including down to zero when there's no traffic, with no cold starts. Launched in 2012, it powers Amazon properties such as Alexa and Amazon.com sites during events like Prime Day, and Amazon says it serves hundreds of customers with tables over 200 TB.
MongoDB's model and its licence
MongoDB stores data in flexible, JSON-like documents, so fields can vary from one document to the next and the structure can change over time. The document model maps to the objects in your application code, and you get ad hoc queries, indexing and real-time aggregation, with high availability, horizontal scaling and geographic distribution built in. There are drivers for more than ten languages.
On licensing, MongoDB's page says the database server is published under the Server Side Public License, with older versions released before its 2018 change under the AGPL, and commercial licences are available through MongoDB Enterprise Advanced if SSPL doesn't satisfy your legal team. Drivers use the Apache License 2.0.
What the free tiers cover
DynamoDB's free tier, per Region and per payer account each month, includes 25 write capacity units, 25 read capacity units, 25 GB of data storage and 2.5 million DynamoDB Streams read requests. Amazon says that's enough for about 200M requests a month, depending on item size, and suits personal apps, prototypes or learning. MongoDB Atlas's Free tier is described as free forever for learning and exploring, with 512MB of storage on shared RAM and vCPU, and you can also download the self-managed Community Edition.
Decide with these questions
- Is your whole stack on AWS? DynamoDB slots in with no servers to run.
- Do you need to run on premises or on several clouds? MongoDB can be self-managed anywhere.
- Will you query data in many unplanned ways? MongoDB's ad hoc queries and aggregation help.
- Do you want zero upgrade work? DynamoDB has no versions or maintenance windows.
- Does your legal team need to review licences? Read MongoDB's SSPL terms first.
For the business side of the choice, read my piece on choosing a good database for your business, and if you're building AI features on AWS, see what AWS Bedrock does.
My advice on DynamoDB or MongoDB
If you're building on AWS and know your access patterns, DynamoDB's no-servers, no-versions model saves a lot of work and its free tier covers early traffic. If you want the freedom to run the same database anywhere, or your team needs flexible queries over documents, MongoDB is the more adaptable choice, and Atlas Free is an easy way to start. Don't choose on the free tier alone; choose on where you'll run in two years.
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Frequently asked questions
Is DynamoDB free?
DynamoDB has a free tier each month that includes 25 GB of storage and 25 read and 25 write capacity units per Region per payer account. Beyond that you pay for what you use.
Is MongoDB free?
MongoDB says it's free to use. MongoDB Atlas has a Free tier with 512MB of storage, and the Community Edition can be self-managed.
Does DynamoDB need upgrades?
No. Amazon's developer guide says DynamoDB has no major, minor or patch versions and no maintenance windows.
What licence does MongoDB use?
MongoDB's server is published under the Server Side Public License v1. Its drivers use the Apache License 2.0, and commercial licences are available.
Can MongoDB run outside a cloud?
Yes. You can run MongoDB in the MongoDB Atlas cloud or self-manage it, including the Community Edition.
