Technology · Free tool
Error Budget Calculator
A service level objective only becomes useful when people know what it allows in practice. This calculator converts an SLO percentage and the number of minutes in a month into the minutes of downtime the error budget permits. It is built for engineering managers, SREs and the business owners who sign off on availability targets and want to know what 99.9% really means.
- OutputAllowed downtime
- No sign-up
- Copy or print the result
- How it works ↓
Your entries stay in this browser. Use Fill example to see a finished page first.
What this technology tool gives you
The result shows allowed downtime in minutes, next to the monthly minutes and the SLO you entered, with the formula underneath. Use it when setting a target, or during a monthly review to compare actual downtime against the budget and decide whether the team should prioritize reliability work.
What you enter
- Minutes in the month: for example 43,200 for a 30-day month
- SLO: the availability target as a percentage, between 0 and 100
Worked example
Using the tool's example, a 43,200-minute month with a 99.9% SLO gives 43,200 × (1 − 0.999) = 43.2 minutes of allowed downtime. The output shows Allowed downtime: 43.20 minutes, Monthly minutes: 43,200 and SLO: 99.90%. That is the most downtime the month can absorb before the objective is missed.
How is an error budget calculated?
Allowed downtime = monthly minutes × (1 − SLO ÷ 100). The result is rounded to two decimal places.
A 30-day month has 43,200 minutes (30 × 24 × 60). A 31-day month has 44,640. The tool uses whatever minute count you enter, so you can apply it to a week, a quarter or a custom window by entering that period's minutes instead.
Tips before you use the result
- Match the minutes to the window in your SLO definition; a 31-day month has 1,440 more minutes than a 30-day month.
- Each extra nine shrinks the budget tenfold: 99.99% on the same month allows 4.32 minutes, which is shorter than most incident responses.
- Compare the budget with the Uptime tool's result for the same period to see how much budget you have used.
- Agree up front what the team does when the budget runs out, such as pausing risky releases, so the number drives a decision.
Frequently asked questions
How much downtime does 99.9% uptime allow?
On a 30-day month of 43,200 minutes, a 99.9% target allows 43.2 minutes of downtime. On a 31-day month of 44,640 minutes it allows 44.64 minutes. Enter your own month length and SLO in the calculator to get the exact figure for your service window.
What is an error budget?
An error budget is the amount of unreliability a service level objective permits over a period. If the SLO is 99.9%, the remaining 0.1% of the period is the budget. Teams use it to balance feature work against reliability: while budget remains, they ship; when it is spent, they stabilize.
Can I use this for a quarter or a week?
Yes. The formula works for any period. Enter the number of minutes in that window instead of a month; a 7-day week is 10,080 minutes, a 90-day quarter is 129,600. The allowed downtime that comes back then covers that same window rather than a month.
Does the calculator keep my SLO numbers?
Your inputs are remembered locally in the browser you are using, without an account, so they are there when you return on the same device. Nothing is sent to a server. Use Clear to reset or Fill example to reload the 99.9% case.
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Results depend on the figures you enter; check them against your own records before you rely on them. Last updated: October 2026 · Kurums editorial team.