SLO Error Budget Calculator (Downtime and Burn Rate)
Enter the SLO, the window and your traffic and errors so far.
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SLO Error Budget Calculator (Downtime and Burn Rate) by TheCalcTools
How the SLO Error Budget Calculator (Downtime and Burn Rate) works
An SLO of 99.9% leaves an error budget of 0.1%: over 30 days that is about 43 minutes of downtime or 0.1% of requests failing. Teams spend the budget on releases and experiments and slow down when it runs low.
Burn rate compares how fast you are using the budget with the even pace: above 1 means you will run out before the window ends.
The formula
Worked example
Using the default values shown in the calculator:
| SLO target | 99.9 % |
|---|---|
| SLO window (days) | 30 |
| Requests in the window (expected) | 5e+07 |
| Failed requests so far | 18000 |
| Days elapsed in the window | 12 |
- 99.9% over 30 days allows 43.2 minutes of downtime or 50,000 failed requests.
- 18,000 failures after 12 days uses 36.0%: burn rate 0.90.
Result:
| Allowed downtime in the window | 43.2 minutes |
|---|---|
| Allowed failed requests | 50,000 |
| Budget used | 36.0% |
| Burn rate (1 = on pace to use exactly the budget) | 0.90 |
| Failed requests left | 32,000 |
Frequently asked questions
How much downtime is 99.99%?
About 4.3 minutes a month or 52.6 minutes a year.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.