API Rate Limit Headroom Calculator
See how much request budget each active user gets under a shared rate limit and how much burst room remains. Input the provider's per-minute cap and your concurrent user count; optionally add average requests per user to gauge throttling risk.
Simplified sizing guide. Confirm enforcement rules with your API provider and add backoff to production clients before load testing.
Examples
- 60,000 req/min limit, 250 active users, 3 req/min each ⇒ Headroom per active user: 240.00 req/min • Projected demand: 750 req/min (1.25% of limit) • Burst margin before throttling: 59,250 req/min.
- 10,000 req/min limit, 900 users, avg requests blank (defaults to 1) ⇒ Headroom per active user: 11.11 req/min • Projected demand: 900 req/min (9.00% of limit) • Burst margin before throttling: 9,100 req/min.
FAQ
How should I pick active users?
Use peak concurrency from logs or dashboards, not total registered users, to size worst-case contention for the shared limit.
Does this account for rolling windows?
No. It assumes a fixed 60-second window. For rolling windows, keep per-user headroom lower and add jitter to client retries.
Can I model multiple API keys?
Run the calculation for each key separately using its own limit and active user pool, then sum projected demand if clients fail over between keys.
Additional Information
- Average requests default to 1 per user per minute when left blank to keep the model conservative.
- Headroom per user is the global limit divided by concurrent users, helpful for client-side throttling guidance.
- Burst margin shows how many extra calls fit in the minute before hitting the provider's ceiling.