SLO Error Budget Calculator

An error budget is the maximum amount of downtime or errors you're allowed to have while still meeting your SLO. If your SLO is 99.9% availability, your error budget is 0.1% — which equals 43.8 minutes per 30-day month. Once consumed, you should stop risky deployments until the next window.

Burn rate tells you how fast you're consuming your error budget relative to the allowed rate. A burn rate of 1.0 means you're consuming budget exactly on pace to exhaust it by end of window. A burn rate of 2.0 means you'll exhaust budget in half the window. Google SRE recommends alerting at 2x burn (6h alert) and 5x burn (1h alert).

Google's Alerting on SLOs chapter defines three windows: 14.4x burn rate over 1 hour (fast burn — page immediately), 6x burn rate over 6 hours (medium burn — ticket urgently), and 3x burn rate over 72 hours (slow burn — create a task). These are starting points; tune based on your SLO window and risk tolerance.

Error budget minutes = (1 - SLO%) × window days × 24h × 60min. For 99.9% over 30 days: (1 - 0.999) × 30 × 24 × 60 = 43.2 minutes. This is the total time your service can be unavailable or erroring before violating the SLO for that period.

When budget hits 0%: freeze all non-critical deployments, halt experiments, focus engineering on reliability improvements. Resume normal velocity only when budget recovers (next window starts or current incident resolves). Some orgs enforce this automatically via deploy gates that check remaining budget.