The Mailchimp Marketing API allows 10 simultaneous connections per user, rather than a set number of calls per minute. Go over and you'll get a 429 error. Calls also time out after 120 seconds, and the Batch endpoint adds a cap of 500 pending batch webhook events per user.
There's no per-minute number to look up
Most APIs publish a requests-per-minute number you can plan around. The Marketing API doesn't. It limits how many connections you have open at the same moment: 10 for each user. That limit is per user, not per API key or per client, so creating a second key doesn't give you a second allowance.
This changes how you think about speed. Ten quick calls finishing in a fraction of a second each leave lots of room. Ten slow calls that each take a minute block you for that whole minute. As the error docs put it, the time a request takes affects how many requests you can make in a given period.
The limits that apply
| Item | Limit | Applies to |
|---|---|---|
| Simultaneous connections | 10 | Each user, Marketing API |
| Call timeout | 120 seconds | Marketing API |
| Pending batch webhook events | 500 | Each user, Batch endpoint |
| Response when over the connection limit | HTTP 429 TooManyRequests | Marketing API |
| Limit increase | Not available per customer | Marketing API |
These cover the Marketing API only. The Transactional product is separate and has its own rules.
Timeouts can use up your connections
Here's the trap. The Mailchimp Developer docs explain that a request can time out on your side but still be running on Mailchimp's backend, and while it's running it still holds one of your connections. So a script that gives up after 30 seconds and immediately retries can end up with the old request and the new one both open. Do that a few times and all 10 slots are full, even though your code thinks it only has one call in flight.
The 120-second timeout on API calls is the outer edge. If your calls regularly get close to it, they're doing too much at once.
What happens when you go over
Reach the connection limit and you'll get a 429. At exceptionally high volumes, the response may be an HTTP 429 or 403 without a JSON body, so don't rely on parsing an error message to spot it. More seriously, the docs say exceeding the limits can result in your API access being disabled, and there's currently no option to raise the limit for an individual customer.
Bulk work without hitting the ceiling
For big jobs, such as syncing a whole list or updating thousands of contacts, the Batch endpoint is the documented route. Long-running requests that still time out despite pagination can be sent there instead. It has its own cap: a maximum of 500 pending batch webhook events per user, and submitting a batch while 500 or more are outstanding returns a 429.
- Cache values that are read often and rarely change, such as list IDs, merge fields and interest groups.
- Use pagination and partial responses so each call asks only for what it needs.
- Send long jobs to the Batch endpoint and keep an eye on pending batch webhook events.
- Let a request finish or fail before sending the same one again.
If you're syncing from a store or a CRM, it's worth counting how many processes share the same Mailchimp user. Three integrations each opening five connections will trip the limit together, even if each one looks well behaved on its own.
How other email platforms throttle
MailerLite's API has a global rate limit of 120 requests per minute and returns 429 Too Many Attempts when you go over. Klaviyo uses two fixed windows, burst (1 second) and steady (1 minute), with tiers from XS at 1 per second and 15 per minute up to XL at 350 per second and 3500 per minute. Brevo documents three tiers of rate limits, general, advanced and extended, with rate limit headers.
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My advice for developers and agencies
Plan for a maximum of 8 connections open at once per Mailchimp user, leaving two spare. Set timeouts longer than your typical call and never retry a request that might still be running. Cache anything that doesn't change daily, and move bulk jobs to the Batch endpoint. If several tools connect to one account, give the heaviest one its own user.
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Frequently asked questions
What is the Mailchimp API rate limit?
10 simultaneous connections per user for the Marketing API.
What happens if I exceed it?
You get a 429 error; at very high volume a 429 or 403 may arrive without a JSON body.
Can I get a higher limit?
No. Mailchimp says there's no option to raise the limit per customer.
What is the timeout?
120 seconds on Marketing API calls.
How do I handle bulk work?
Use the Batch endpoint, keeping under the 500 pending batch webhook events cap, and cache data that rarely changes.
