Uptime calculator
Calculate the downtime an uptime or availability target allows, or turn minutes of downtime back into a percentage. See what 99.9% actually promises.
99.9% uptime allows 8h 45m 58s of downtime a year. A month is taken as 30.44 days and a year as 365.25.
Site down - example.com
example.com is not responding: HTTP 503 from https://example.com/.
Would you know if your site went down tonight?
An uptime target is only a number until something measures it. Upcheck checks every site every 5 minutes and alerts you by Email, Slack, Discord, Teams, or Webhook when it stops answering.
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What a percentage means in minutes
An uptime figure like 99.9% is a promise about how much of a period a service may be unavailable, and it is much easier to reason about as a duration: 99.9% is about 43 minutes a month, 99.99% is about 4 minutes, and 99.999% is 26 seconds. This calculator does the conversion in both directions, taking a month as 30.44 days and a year as 365.25 days so the figures match the way most SLAs are measured.
The calculator tells you the budget. Knowing whether you are inside it means measuring, and Upcheck checks every website every 5 minutes, confirms an outage before alerting, and keeps the history.
Two inputs, no signup
- 01
Enter a percentage
Type an uptime target or pick a preset from 90% to five nines.
- 02
Or enter minutes of downtime
Type the downtime you had, or can tolerate, in a month and the percentage updates to match.
- 03
Read the budget
Allowed downtime for every period, computed as you type, with the assumptions stated.
Frequently asked questions
How much downtime is 99.9% uptime?
About 1 minute 26 seconds a day, 10 minutes a week, 43 minutes 50 seconds a month, and 8 hours 46 minutes a year. Three nines is the most common SLA for hosted services, and it is looser than it sounds: a single bad deploy can spend a month's budget in one afternoon.
How much downtime is 99.99% uptime?
About 8.6 seconds a day, 1 minute a week, 4 minutes 23 seconds a month, and 52 minutes 36 seconds a year. Four nines is what serious infrastructure providers offer and it leaves essentially no room for manual intervention: detecting an outage, waking someone, and fixing it in four minutes is not realistic, so hitting it means automatic failover.
How do I calculate uptime percentage?
Divide the time the service was available by the total time in the period, then multiply by 100: a service down for 22 minutes in a 30-day month was up for 43,778 of 43,800 minutes, which is 99.95%. The calculator does it in both directions, so entering the minutes you were down gives the percentage, and entering a percentage gives the minutes it allows. The figure is only as good as what you measured it with: uptime worked out from the outages you happened to notice is always higher than uptime measured by checking from outside on a schedule.
What are 'the nines'?
Shorthand for uptime percentages by the number of nines they contain: two nines is 99% (about 7 hours a month down), three is 99.9% (44 minutes), four is 99.99% (4 minutes), five is 99.999% (26 seconds). Each extra nine cuts the budget by ten and roughly multiplies the engineering cost by more than that.
Why does the calculator use 30.44 days for a month?
Because months vary and SLAs are usually written per month without saying which one. 30.44 is the average length of a month over the year (365.25 ÷ 12), and the year is 365.25 days to account for leap years. Providers that measure per calendar month will show slightly different figures for February and for 31-day months.
Does scheduled maintenance count as downtime?
It depends on the SLA. Most providers exclude announced maintenance windows from the calculation, which is why an advertised 99.95% can coexist with an hour of planned downtime a month. Read the definitions section of any SLA before comparing numbers, and measure from outside with your own monitoring rather than relying on the provider's own status page.
How do I know my actual uptime?
By checking from outside on a schedule and recording every failure. Upcheck requests every website you add every 5 minutes, confirms an outage on a second probe so a blip doesn't count, keeps the history, and alerts your team by email, Slack, Discord, Teams, or webhook when a site goes down and when it recovers.
The calculator gives you the budget. Monitoring tells you what you spent.
Add your websites to Upcheck and find out, in real numbers, whether you are inside your SLA.