Uptime Calculator
This free uptime calculator turns an uptime percentage into the downtime it allows per day, week, month, quarter and year. For example, 99.9% uptime allows about 8 hours 45 minutes of downtime a year, or 43 minutes in a typical month.
Uptime percentage to downtime
Downtime to uptime percentage
The nines at a glance
| Uptime | Per day | Per month | Per year |
|---|---|---|---|
| 90% | 2h 24m 0s | 3d 1h 3m 0s | 36d 12h 36m 0s |
| 99% | 14m 24s | 7h 18m 18s | 3d 15h 39m 36s |
| 99.5% | 7m 12s | 3h 39m 9s | 1d 19h 49m 48s |
| 99.9% | 1m 26s | 43m 49s | 8h 45m 57s |
| 99.95% | 43s | 21m 54s | 4h 22m 58s |
| 99.99% | 8s | 4m 22s | 52m 35s |
| 99.999% | 0s | 26s | 5m 15s |
Worked out in your browser. Nothing you enter is sent to us. A month is counted as one twelfth of a 365.25-day year, about 30.44 days.
Free, no signup.
What does 99.9% uptime really mean?
Uptime is the share of a period when a service is working. 99.9% sounds almost perfect, but the 0.1% that is left adds up: over a 365.25-day year it is 8 hours, 45 minutes and 57 seconds. Over a day it is only a minute and a half, which is why a single short blip can use up a big part of the day's allowance.
Each extra nine cuts the allowance by ten. 99% allows about 3 days 15 hours a year, 99.99% allows about 52 minutes, and 99.999% (five nines) allows barely 5 minutes. The table above shows the whole ladder. Every extra nine usually costs a lot more to deliver, so pick the level your site really needs, not the biggest number.
Reading an SLA: what counts as downtime
A service level agreement, or SLA, is a written promise about availability, usually with a remedy such as a service credit if the provider misses it. The percentage alone tells you very little. The small print decides what the number is worth.
Look for what counts as downtime and what does not. Many SLAs exclude planned maintenance, problems caused by your own code or settings, attacks and events outside the provider's control. Check whether partial outages count, how the outage is measured and who measures it, how quickly you have to report a problem, and whether the remedy is automatic or you have to claim it. A credit is usually a small share of your monthly fee, not compensation for lost sales.
Monthly versus yearly measurement
The same percentage gives very different room to fail depending on the window. 99.9% measured per month allows around 43 minutes in that month. Measured per year it allows nearly 9 hours, and a provider could in theory use most of that in a single bad day and still meet the target.
Shorter windows are stricter and usually better for you, because one long outage cannot hide inside a year of good days. When you compare two plans, convert both to the same period first. This calculator does that for you, and the second box works the other way: enter an outage and a period and it gives you the percentage you actually got.
How to measure your own uptime
Do not rely only on the provider's own status page. Run an outside monitor that requests your site every minute or so from more than one place, and checks for a correct response, not just a connection. Keep the log. When something goes wrong you will have times to point to.
Then add up the minutes of failed checks over the period and put them into the second box above to get your real percentage. Remember that a monitor checking every five minutes can miss short outages, and that a page can load while checkout or login is broken. For important flows, check those pages as well as the home page.
Frequently asked questions
How much downtime is 99.9% uptime?
About 8 hours 45 minutes a year, 43 minutes in an average month, 10 minutes a week and 1 minute 26 seconds a day. It is often called three nines.
What is the difference between 99.9% and 99.99% uptime?
Ten times less downtime. 99.9% allows nearly 9 hours a year, while 99.99% allows about 52 minutes. The extra nine is much harder and more expensive for a provider to deliver.
Is 100% uptime possible?
Not in practice. Hardware fails, networks drop and software needs updates. Be careful with any promise of 100%, and read the small print to see what is excluded.
How do I calculate uptime percentage?
Divide the minutes the service was down by the minutes in the period, multiply by 100, and subtract the result from 100. The second box in the calculator does the sum for you.
Does planned maintenance count as downtime?
It depends on the SLA. Many agreements exclude announced maintenance windows from the calculation, so the percentage can look better than what your visitors experienced. Check the wording.
Why do you count a year as 365.25 days?
It averages in leap years, so every year and every month is treated the same. Some providers use 365 days or a 30-day month, which changes the result by a few seconds or minutes.
Is anything I type sent to a server?
No. The sums run in your browser and nothing you enter is uploaded. Only the percentage is written to the page address so you can share a link.
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