Error Budget Calculator
Calculate the allowed downtime (error budget) for a given SLO target over a chosen time period, e.g. 99.9% over 30 days.
Inputs
The service level objective, e.g. 99.9% availability.
The measurement window for the SLO (commonly 28 or 30 days).
Downtime already consumed in the current period, to compute remaining budget.
Error Budget
43.20minutes
Error Budget
0.720hours
Remaining Budget
43.20minutes
Budget Consumed
0.0%
Budget Exhausted
false
Step by step
Time period in minutes
30 × 24 × 60
= 43,200 min
Allowed downtime fraction: 1 − SLO
1 − 99.9/100
= 0.001000
Error budget: fraction × period
0.001000 × 43,200 min
= 43.20 min
Remaining budget: budget − downtime so far
43.20 − 0
= 43.20 min
How it works
An error budget is the amount of unreliability an SLO permits: budget = (1 − SLO) × time_period. For example, a 99.9% SLO over a 30-day period allows (1 − 0.999) × 30 × 24 × 60 = 43.2 minutes of downtime. Tracking consumption against this budget lets teams make data-driven decisions about when to slow down feature velocity in favor of reliability work.
Formula
errorBudget = (1 - sloTarget / 100) × timePeriodMinutes
- S
- SLO target percentage (e.g. 99.9)
- T
- Time period in minutes
- E
- Error budget in minutes of allowed downtime
Frequently Asked Questions
What's the error budget for 99.9% over 30 days?
(1 − 0.999) × 30 days × 1440 minutes/day = 43.2 minutes — this is the classic 'three nines' monthly budget cited in SRE literature.
What happens when the error budget is exhausted?
Most SRE practices freeze non-essential feature releases and prioritize reliability work until the service is back within its SLO for the measurement window.
Should error budget be measured in requests or time?
Time-based budgets suit availability SLOs; request-based budgets (bad requests / total requests) suit success-rate SLOs. Use whichever matches how your SLO is defined.
How does error budget relate to burn rate?
Burn rate is the speed at which you're consuming the error budget relative to the time elapsed in the period — a burn rate of 1x means you'll exhaust the budget exactly at period end; faster burn rates trigger earlier alerting.