Uptime & SLA calculator
Enter an uptime percentage or pick a common SLA target and instantly see how much downtime it allows per day, week, month and year. You can also work backwards: type the minutes of downtime you had and read off the resulting uptime percentage. Everything is calculated in your browser - nothing is sent to our server.
Edit either field. Changing the percentage updates the downtime, and changing the downtime updates the percentage. A month is taken as 30 days and a year as 365 days.
The nines: uptime cheat sheet
Each extra nine cuts the allowed downtime by roughly ten times. This table shows the maximum downtime for the most common SLA levels.
| Uptime | Nines | Per day | Per month | Per year |
|---|---|---|---|---|
| 99% | Two nines | 14m 24s | 7h 12m | 3d 15h 36m |
| 99.9% | Three nines | 1m 26s | 43m 12s | 8h 45m 36s |
| 99.95% | Three and a half nines | 43s | 21m 36s | 4h 22m 48s |
| 99.99% | Four nines | 8.6s | 4m 19s | 52m 34s |
| 99.999% | Five nines | 0.86s | 26s | 5m 15s |
How the uptime calculator works
Uptime is the share of time a service is available. Downtime is everything that is left over. If a service is available 99.9 percent of the time, it is unavailable 0.1 percent of the time, and this calculator turns that 0.1 percent into real hours and minutes for each period.
The maths is simple: downtime equals the length of the period multiplied by one minus the uptime fraction. For a year of 365 days that is 525600 minutes, so 99.9 percent uptime allows 525.6 minutes of downtime, which is about 8 hours and 46 minutes per year.
The reverse calculation is just as useful. If you already know how many minutes of downtime you had in a month, the tool divides that by the minutes in a month and subtracts from 100 percent to give you the uptime figure you can report.
How to read the result
The four boxes show the allowed downtime for the chosen uptime level across different periods. Use them to decide which SLA you can realistically promise or expect.
- Higher percentages mean less downtime but are far harder and more expensive to guarantee.
- Per month is the figure most SLA contracts use, because monthly billing periods are common.
- Per year shows the cumulative impact and is the easiest number to grasp intuitively.
Why uptime targets matter
Choosing an SLA to promise. Before you commit to an uptime figure in a contract, check how little downtime it leaves you. Promising 99.99 percent gives you under 53 minutes a year for all maintenance and incidents combined.
Checking whether you met your SLA. Add up your downtime minutes for the month, enter them here and read off your real uptime. If it is below your promised figure, you may owe service credits.
Comparing providers. Vendors love to quote nines. This calculator translates marketing numbers into concrete downtime so you can compare offers on equal terms.
Frequently asked questions
What does 99.9 percent uptime actually mean?
It means the service may be unavailable for at most 0.1 percent of the time. Over a year that is about 8 hours and 46 minutes, and over a month about 43 minutes and 12 seconds.
How do you calculate allowed downtime?
Take the length of the period and multiply it by one minus the uptime fraction. For example, 99.95 percent over a 30 day month is 43200 minutes times 0.0005, which is 21.6 minutes, or about 21 minutes and 36 seconds.
Do you count a month as 30 or 31 days?
This calculator uses 30 days for a month and 365 days for a year, which are the most common conventions in SLA contracts. If your contract defines a calendar month, multiply accordingly.
Is this calculator free and private?
Yes. It is free, needs no account and runs entirely in your browser. No URL or value is sent to our servers, so you can use it for confidential SLA figures.
Turn targets into real, measured uptime
A calculator tells you what an SLA allows. ePulz.io measures your actual uptime around the clock, records every incident and gives you the reports you need to prove it.
Start monitoring freeAbout this tool
The uptime and SLA calculator is one of several free tools from ePulz.io. It converts any uptime percentage into allowed downtime per day, week, month and year, and works in reverse from downtime minutes to a percentage. All calculations run in your browser.