Burn rate is how fast a service is using up its error budget, compared with the pace that would use it exactly by the end of the SLO window. A burn rate of 1 spends the whole budget in the window; 10 spends it ten times faster.
Formula
Burn rate
burn rate = observed error rate ÷ (1 − SLO target)Time to exhaustion
time to exhaustion = SLO window ÷ burn rateWorked example
SLO 99.9% over 30 days, so the allowed error rate is 0.1%. Over the last hour 0.5% of requests failed. Burn rate = 0.5 / 0.1 = 5. At that pace the budget is gone in 30 / 5 = 6 days.
What each burn rate means
| Burn rate | 30-day budget gone in | What it usually means |
|---|---|---|
| 1 | 30 days | On pace |
| 2 | 15 days | Slow leak; open a ticket |
| 6 | 5 days | Serious; act within hours |
| 14.4 | about 2 days | Urgent; act now |
| 36 | 20 hours | Severe outage |
- 1×30 daysOn pace
- 2×15 daysSlow leak
- 6×5 daysSerious
- 14.4×~2 daysUrgent
- 36×20 hoursSevere outage