Error Budget (SLO) Calculator
Turn a service-level objective into an error budget: how much downtime you can spend per month, week and day before you breach the SLO.
How it works
Error budget = window × (100% − SLO) · e.g. minutes = window days × 1440 × (1 − SLO/100)
An SLO of 99.9% availability is the same as an error budget of 0.1% — the amount of unavailability you are allowed to spend before you have broken your promise. Expressing it as concrete downtime per window makes the trade-off tangible: teams that have budget left can ship faster and take risks, while a spent budget signals a freeze to focus on reliability. Each added nine cuts the allowed downtime by roughly ten times.
Worked example
A 99.9% SLO over 30 days: the window is 30 × 1,440 = 43,200 minutes, and 0.1% of that is 43.2 minutes of allowed downtime — about 10 minutes a week or 1.44 minutes a day.
Sources: Google SRE Book — Embracing Risk
Frequently asked questions
What is the difference between an SLO and an error budget?
The SLO is the target (say 99.9% available); the error budget is the complement — the 0.1% of failure you are permitted. The budget reframes reliability as a spendable resource rather than an absolute.
How much downtime does each "nine" allow?
Over 30 days: 99% ≈ 7.2 hours, 99.9% ≈ 43 minutes, 99.99% ≈ 4.3 minutes, 99.999% ≈ 26 seconds. Every extra nine is roughly ten times stricter.
Should the budget count downtime or failed requests?
Either, depending on how you measure the SLO. Time-based SLOs count minutes of unavailability; request-based SLOs count the fraction of failed requests. This calculator shows both a duration and the equivalent request fraction.
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This calculator is for educational purposes. Double-check important results before acting on them.