How to use the API Rate Limit
- Enter the API's limit and its window length.
- Enter your expected request volume over the same period.
- Add your concurrency or worker count.
- Read the required delay between requests and whether bursts will trip the limit.
How the calculation works
The sustainable rate is limit ÷ window seconds; the minimum spacing between requests is its reciprocal, multiplied up by the number of parallel workers so they share the budget. A 600-per-minute limit is 10 per second, so five workers each need a 500 ms gap. Ignoring concurrency is the usual reason a job that tested fine gets throttled in production.
Most providers implement a token bucket: tokens refill at a steady rate up to a bucket size, so short bursts above the average rate are tolerated until the bucket empties. Fixed-window limiters instead allow up to twice the limit across a window boundary, then block. When a 429 arrives, honour the Retry-After header; otherwise use exponential backoff with jitter, since synchronised retries from many clients recreate the spike that caused the throttle.
Rate = limit / window seconds ; delay per worker = workers / rateSource: Token bucket and fixed-window rate limiting algorithms; HTTP 429 and Retry-After per RFC 6585.
Worked example
Processing 90,000 records against a 1,200 requests-per-minute limit using 8 workers.
- Sustainable rate = 1,200 / 60 = 20 req/s.
- Total time = 90,000 / 20 = 4,500 s = 75 minutes.
- Per-worker delay = 8 / 20 = 400 ms between requests.
- Burst of 8 simultaneous calls consumes 8 tokens instantly — safe if the bucket holds ≥ 8.
About 75 minutes minimum, with each worker pausing 400 ms between calls to stay inside the limit.
Frequently asked questions
What does HTTP 429 mean?+
Too Many Requests — you exceeded the limit. Check the Retry-After header before retrying.
Why do I get throttled below the limit?+
Usually concurrency: parallel workers share one budget, so eight workers at the single-worker rate send eight times too fast.
What is jitter and why add it?+
Random variation in backoff delays. It stops many clients retrying in lockstep and recreating the spike.
Are limits per key or per IP?+
It varies. Check the provider's documentation — some apply both, and some count per endpoint.
Last reviewed August 31, 2026. We review this page whenever the underlying formula, tax year, published rate or standard changes.