Serverless Reserved Concurrency Budget Calculator

Prevent cold starts and throttles by sizing reserved or provisioned concurrency for your busiest serverless workload. Input peak requests per second, runtime, and your platform’s hourly rate to see the concurrency required, buffer headroom, and monthly cost. Optional fields let you adjust coverage hours or override monthly request volume for per-request economics.

Highest sustained request rate you expect during the busiest minute.
Include runtime plus external calls that hold the execution open.
Hourly price per provisioned concurrency unit for your memory size and region.
Optional. Add headroom to absorb traffic spikes without throttling.
Optional. Hours per month you plan to keep provisioned capacity active.
Optional. Override if monthly traffic is lower than peak sustained volume.

Confirm concurrency pricing and throttling rules with your cloud provider before deploying.

Examples

  • 450 req/s peak, 180 ms duration, $0.036 per unit-hour, 20% buffer, 730 hours, default monthly requests ⇒ Peak concurrent executions required: 81.00 • Recommended reserved concurrency with 20.00% buffer: 98 • Monthly provisioned concurrency cost (730 hours): $2,575.44 • Cost per 1,000,000 requests: $0.17 • Idle headroom above peak load: 17.00 concurrent units
  • 120 req/s peak, 250 ms duration, $0.028 rate, buffer 35%, coverage 500 hours, 20 million monthly requests ⇒ Peak concurrent executions required: 30.00 • Recommended reserved concurrency with 35.00% buffer: 41 • Monthly provisioned concurrency cost (500 hours): $574.00 • Cost per 1,000,000 requests: $0.03 • Idle headroom above peak load: 11.00 concurrent units

FAQ

How do I estimate the peak requests per second?

Use recent production monitoring data or load-test results during launch peaks. If seasonality spikes higher, apply that larger rate.

What if traffic is bursty and exceeds the buffer?

Increase the buffer percentage or combine provisioned concurrency with reserved concurrency or on-demand burst strategies to cover outliers.

Does this include invocation and compute charges?

No. Layer in per-request and GB-second costs separately. This tool isolates the fixed cost of keeping capacity warm.

Can I model scheduled scaling windows?

Set provisioned hours to the number of hours you plan to keep concurrency active each month, or average multiple schedules into one blended value.

Additional Information

  • Reserved or provisioned concurrency locks warm environments so Lambda, Cloud Functions, or Azure Functions skip cold starts.
  • Multiply peak requests per second by average runtime (in seconds) to estimate the concurrency footprint you must sustain.
  • Provisioned concurrency pricing varies by memory size and region; confirm the hourly rate before committing to long-term capacity.

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