Free tool

Uptime and SLA Downtime Calculator

99.9% uptime allows about 8 hours 46 minutes of downtime a year, or about 44 minutes a month. Enter any uptime percentage to see exactly how much downtime it allows.

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Allowed downtime for an uptime target

%

Between 0 and 100, for example 99.95.

Per day
1m 26s
Per week
10m 5s
Per month
43m 50s
Per quarter
2h 11m 29s
Per year
8h 45m 58s

Reference table

Downtime Allowed by Common SLA Levels

Maximum downtime allowed per period for common uptime percentages
UptimePer dayPer monthPer year
99%14m 24s7h 18m 18s3d 15h 39m 36s
99.5%7m 12s3h 39m 9s1d 19h 49m 48s
99.8%2m 53s1h 27m 40s17h 31m 55s
99.9%1m 26s43m 50s8h 45m 58s
99.95%43s21m 55s4h 22m 59s
99.99%9s4m 23s52m 36s
99.999%1s26s5m 16s

A year is 365.25 days and a month is 30.44 days (a year divided by 12). Figures are rounded to the nearest second.

How to read it

Each extra "nine" cuts the allowed downtime by roughly ten times. 99% allows more than three and a half days of downtime a year; 99.99% allows under an hour. The month column is usually the one that matters, because most SLAs measure uptime per calendar month and reset at the start of the next one.

From downtime to uptime

min

99.8996% uptime that month

Combined SLA of dependent services

If your service needs all of these to be up (for example hosting, database and payments), their uptimes multiply.

%
%

99.94% combined, about 26m 18s of downtime a month

SLA credits

What Happens When an SLA Is Missed

An SLA is usually a promise backed by service credits, not cash refunds. If a provider misses its monthly target, you can typically claim a credit worth a percentage of that month's bill, with bigger credits for bigger misses. Most providers require you to claim within a set window and to show when the outage happened, and planned maintenance is often excluded. The exact percentages and rules differ by provider, so check the SLA document itself. Our guide to uptime SLAs and the glossary entry on SLAs go deeper.

Detection time eats into your budget

At 99.9%, you have about 44 minutes of downtime a month. If your monitor checks every 5 minutes, an outage can run up to 5 minutes before the first failed check, which is already more than a tenth of that budget. Monitoristic checks every 5 minutes on Lite, every 2 minutes on Pro and every minute on Business, and alerts you on Telegram or by webhook as soon as a check fails. The uptime history it records is also the evidence you need for an SLA credit claim. See plans.

FAQ

Uptime and SLA Questions

What does 99.9% uptime mean? +
It means the service may be unavailable for up to 0.1% of the time: about 1m 26s a day, 43m 50s a month, or 8h 45m 58s a year.
How much downtime does a 99.99% SLA allow? +
About 4m 23s a month, or 52m 36s a year. That is short enough that a single slow-to-detect outage can use up a whole month's budget.
Why does each extra nine matter so much? +
Each nine cuts the allowed downtime by about ten times: 99.9% allows roughly 44 minutes a month, 99.99% about 4 minutes, and 99.999% under 30 seconds.
How do I calculate the combined uptime of several services? +
If your service needs all of them to work, multiply their uptimes as decimals. For example, 99.99% × 99.95% = 0.9999 × 0.9995 ≈ 99.94% combined, which is lower than either one on its own.
Does planned maintenance count as downtime? +
It depends on the SLA. Many providers exclude scheduled maintenance announced in advance, so read the definitions section of the SLA. For your own reporting, Monitoristic maintenance windows keep planned work from triggering alerts.
How do I prove downtime for an SLA credit? +
Providers usually ask for the start and end time of the outage. An external uptime monitor gives you timestamped check history and incident records you can attach to the claim.

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