Technology · Free tool
Uptime Percentage Calculator
Service level reports, customer SLAs and board updates all ask the same question: what was our availability last period? This calculator turns the minutes a service was down and the length of the period into an uptime percentage. It is meant for engineering managers, customer success teams and finance leads checking service credits against a contract.
- OutputUptime percent
- 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 output shows uptime as a percentage to two decimals, with the minutes down and the minutes in the period beside it and the formula below. Put it in a monthly service review, or compare it with the error budget from your SLO to see whether the target was met.
What you enter
- Minutes down: total minutes of downtime in the period
- Minutes in the period: for example 43,200 for a 30-day month
Worked example
In the example, a service was down for 50 minutes in a 43,200-minute month. Uptime = (43,200 − 50) ÷ 43,200 × 100 = 99.88%. The output shows Uptime: 99.88%, Minutes down: 50 and Minutes in the period: 43,200. Against a 99.9% SLO, which allows 43.2 minutes, that month missed the target.
How is uptime percentage calculated?
Uptime = (minutes in the period − minutes down) ÷ minutes in the period × 100, rounded to two decimals.
Minutes down cannot be larger than the minutes in the period, and neither value can be negative. If the period is zero, the tool warns that there is no divisor instead of returning a number.
Tips before you use the result
- Agree what counts as down before you measure: full outage only, or also partial degradation.
- Check whether your SLA excludes scheduled maintenance; if so, subtract those minutes from downtime first.
- Use the exact period length: February and a 31-day month give different results for the same downtime.
- Look at two decimals when targets are close to 100%; 99.88% and 99.9% sound similar but one misses a three-nines target.
Frequently asked questions
How do you calculate uptime percentage?
Subtract the minutes of downtime from the total minutes in the period, divide by the total minutes and multiply by 100. For 50 minutes down in a 30-day month of 43,200 minutes, uptime is 99.88%. The calculator does this for any period you enter and rounds the result to two decimals.
How many minutes are in a month for uptime?
It depends on the month: 40,320 for 28 days, 43,200 for 30 days and 44,640 for 31 days. Many SLAs use the actual calendar month. Enter the minutes that match the period defined in your contract or in your SLO.
Is 99.9% uptime good?
It depends on what customers expect and what you promised. 99.9% on a 30-day month allows 43.2 minutes of downtime. Higher targets allow much less. The Error budget tool shows the allowed downtime for any target, so you can compare it with the uptime you measured.
Do I need to log in to calculate uptime?
No log-in is required. Both numbers are held in your browser on this device between visits and never leave it. That makes it quick to rerun the calculation each month: change the two values and copy the result into your report.
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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.