Free tool

Uptime & SLA Calculator

Turn an uptime percentage into allowed downtime per day, week, month and year, or work out the uptime from the downtime you had.

Calculator

Allowed downtime at 99.9% uptime:

Per day
1m 26s
Per week
10m 5s
Per month
43m 50s
Per quarter
2h 11m 29s
Per year
8h 45m 57s

Are you meeting 99.9%? UptimeDuck checks your site around the clock and alerts you the moment it goes down.

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SLA downtime table

Allowed downtime for the most common uptime targets. A month is one twelfth of an average year (about 30.44 days).

UptimeDayWeekMonthQuarterYear
90%2h 24m16h 48m3d 1h 2m 55s9d 3h 8m 44s36d 12h 34m 55s
95%1h 12m8h 24m1d 12h 31m 27s4d 13h 34m 22s18d 6h 17m 28s
98%28m 48s3h 21m 36s14h 36m 35s1d 19h 49m 45s7d 7h 18m 59s
99%14m 24s1h 40m 48s7h 18m 17s21h 54m 52s3d 15h 39m 30s
99.5%7m 12s50m 24s3h 39m 9s10h 57m 26s1d 19h 49m 45s
99.8%2m 53s20m 10s1h 27m 39s4h 22m 58s17h 31m 54s
99.9%1m 26s10m 5s43m 50s2h 11m 29s8h 45m 57s
99.95%43s5m 2s21m 55s1h 5m 45s4h 22m 58s
99.99%9s1m4m 23s13m 9s52m 36s
99.995%4s30s2m 11s6m 34s26m 18s
99.999%864ms6s26s1m 19s5m 16s

How the uptime calculation works

Uptime is the share of time a service is available. Allowed downtime is the rest: downtime = period × (1 − uptime %). At 99.9% uptime a service can be unavailable for 0.1% of the time, which is about 1 minute 26 seconds a day or 43 minutes 50 seconds a month.

The reverse works the same way: uptime % = (period − downtime) ÷ period × 100. 45 minutes of downtime in a month is 99.897% uptime, just short of a 99.9% SLA.

Each extra nine cuts the allowed downtime by ten. Going from 99.9% to 99.99% takes a month's budget from about 44 minutes to about 4 minutes, so you need monitoring that notices an outage within a minute or two, not after a customer emails you.

Frequently asked questions

How much downtime is 99.9% uptime?+
99.9% uptime (“three nines”) allows about 1m 26s of downtime per day, 10m 5s per week, 43m 50s per month and 8h 45m 57s per year.
How much downtime is 99.99% uptime?+
99.99% uptime (“four nines”) allows about 9s per day, 1m per week, 4m 23s per month and 52m 36s per year.
What is an SLA percentage?+
A service level agreement (SLA) often promises a minimum uptime over a billing period, such as 99.9% per month. If availability falls below it, the provider usually owes a service credit. The percentage translates directly into a downtime budget for that period.
How long is a month in this calculator?+
A month is one twelfth of an average Gregorian year of 365.2425 days, about 30.44 days. A quarter is a quarter of that year. Contracts sometimes use calendar months instead, so check how your SLA defines the period.
Does scheduled maintenance count as downtime?+
It depends on the agreement. Many SLAs exclude announced maintenance windows, while others count every minute the service is unreachable. The calculator treats all downtime equally.
How do I measure my real uptime?+
Check the service from outside your network at a regular interval and record every failed check. UptimeDuck does this from several regions and shows uptime per monitor, so you can compare it with your SLA. Create a free account to start.

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