How is an error budget calculated?

Error budget = (1 − SLO) × total time in the window. For 99.9% over 28 days that is 0.001 × 40,320 minutes ≈ 40.3 minutes of allowed downtime.

Burn rate = current bad-event rate ÷ (1 − SLO). A burn rate of 1 exhausts the budget exactly at the window's end; higher means faster. It's what should drive alerting urgency.

Error Budget Calculator — SLO to Allowed Downtime & Burn Rate

Free error budget calculator. Turn an SLO target and measurement window into allowed downtime, and compute burn rate from your current bad-event rate.

The math

error_budget = (1 − SLO) × window
burn_rate    = current_bad_rate ÷ (1 − SLO)

Every extra "nine" shrinks the budget by roughly 10×, which is why the cost of each additional nine grows disproportionately. Pick the lowest SLO your users will tolerate, not the highest you can imagine.

Allowed downtime at a glance

SLO	per 28 days	per 30 days
99%	~6.7 hours	~7.2 hours
99.9%	~40 min	~43 min
99.95%	~20 min	~22 min
99.99%	~4 min	~4.3 min

Deeper dives: SLOs and error budgets and calculating an error budget step by step.

Discussions coming soon.

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