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Example — Error Budget Calculator
SLO 99.9% Error Budget: How Much Is Consumed by a 25-Minute Incident?
Calculate the percentage of a 99.9% monthly SLO error budget consumed by a 25-minute incident. Shows remaining budget, burn rate, and multi-window alert thresholds.
Worked example
Input
SLO target: 99.9%
Window: 30 days
Incident duration: 25 minutes
Success rate during incident: 0% (full outage)
Output
SLO Error Budget Calculation
SLO: 99.9% | Window: 30 days
Error budget: 0.1% × 43,200 min = 43.2 minutes
Incident: 25 minutes consumed
Budget used: 25 / 43.2 = 57.9%
Budget remaining: 18.2 minutes (42.1%)
Burn rate during incident: 1.0 (1 minute of budget per minute of outage)
Alert thresholds (multi-window):
Fast burn (1h window, 5% budget): 43.2 × 0.05 = 2.16 min → alert at 2.16 min of outage in 1hr
Slow burn (6h window, 10% budget): 43.2 × 0.10 / 6 = 0.72 min/hr sustained
Status: YELLOW — majority of budget consumed
Remaining capacity: 18.2 minutes of downtime for the rest of the month
A 25-minute full-outage incident consumes 57.9% of a 99.9% monthly error budget, leaving only 18.2 minutes of downtime allowance for the remainder of the month. This triggers a risk posture shift: changes should be reviewed more carefully and the team should increase deployment scrutiny for the rest of the window. The burn rate of 1.0 during the incident means budget is consumed at exactly the natural rate — no amplification.
What to do next
After this incident, freeze non-emergency production changes until the error budget recovers (next window reset) or implement additional safeguards. File a post-mortem to prevent recurrence before the budget is exhausted by a second incident.
Use the Error Budget Calculator to run this on your own input.
What is the difference between burn rate and error budget consumption?
Error budget consumption is absolute: 25 minutes consumed out of 43.2 available. Burn rate is relative: how fast the budget is being consumed relative to the natural depletion rate. A burn rate of 1.0 means budget is consumed at the same rate as time passes. A burn rate of 14.4 means budget depletes 14.4x faster than normal — consuming the monthly budget in ~2 days. Multi-window burn rate alerts catch both fast and slow burns.
How do rolling vs calendar windows affect error budget resets?
Calendar windows (reset on the 1st of each month) are simpler to explain to stakeholders but create perverse incentives near month end — teams may delay risky changes to the beginning of a new window. Rolling 28-day windows smooth this by never having a 'clean slate' moment. Most SRE implementations prefer rolling windows for operational discipline.