Request-Based SLO Error Budget Calculator

Method, formula and assumptions

Whole-request budget = floor(total eligible requests x (1 - SLO fraction)). Subtract observed and forecast bad requests. Observed success = 1 - bad/eligible requests.

Input definitions and supported units

• Total eligible requests in window: Whole-number count, from 1 to 1000000000000; must be positive.
• Target success rate (%): Measured or assumed numerical value, from 0 to 100; zero is supported where the stated method permits it.
• Observed bad eligible requests: Whole-number count, from 0 to 1000000000000; zero is supported where the stated method permits it.
• Forecast additional bad requests: Whole-number count, from 0 to 1000000000000; zero is supported where the stated method permits it.

Worked example with answer

One million eligible requests at a 99.9% target allow 1,000 bad requests. After 400 observed, 600 remain; a forecast of 200 more leaves 400. Observed success is 99.96%.

How to use the results

A negative remaining budget identifies a breach. Forecast is an allocation against the fixed denominator, not new eligible traffic.

Results retain full precision internally and display up to four decimal places. Very small nonzero results use scientific notation rather than appearing as zero. Check the labels before comparing values across units.

Limitations and references

This is request-based, not uptime-based. Define eligibility and failure criteria consistently; rolling-window changes and different request classes are not modeled.

The method is a self-contained arithmetic, geometric or explicitly stated mathematical model. There are no imported tariffs, empirical presets or equipment specifications; measured values and allowances must come from your own process.

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