Feature Flag Rollout Impact Calculator

Quantify how much of your error budget a new feature rollout could consume. Enter traffic, rollout coverage, baseline and expected error rates, plus your daily error budget to see the projected percentage consumed.

Total traffic touching the service each day.
Percent of traffic targeted by the feature flag.
Current failure rate before rollout.
Projected failure rate for exposed traffic while the feature flag is on.
Maximum allowable errors per day to stay within SLO.

Simplifies complex reliability dynamics; validate with production telemetry.

Examples

  • 1,500,000 requests, 25% rollout, 0.3% → 0.6% errors, 5,000 budget ⇒ 45 %
  • 900,000 requests, 40% rollout, 0.2% → 0.35% errors, 3,000 budget ⇒ 42 %

FAQ

Why ignore baseline errors?

Baseline errors are already accounted for in your remaining budget; this model focuses on the flagged traffic contribution.

How do I model gradual ramp-ups?

Run the calculator at several rollout percentages (e.g., 5%, 25%, 50%) to map a safe ramp schedule.

Can I use sessions instead of requests?

Yes. Any consistent traffic unit works as long as the error budget uses the same unit for counting failures.

Additional Information

  • Compare the result with alert thresholds to decide on rollout pacing.
  • Re-run the calculation as you adjust rollout percentage to keep usage under 100% of the budget.
  • Baseline and expected error rates should use the same measurement window as the error budget.

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