Uptime SLA & downtime calculator

A free calculator: type an uptime target and see exactly how much downtime it buys you per day, week, month and year. No sign-up, no math.

uptime target

1m 26s per day

10m 5s per week

43m 12s per month

8h 45m 36s per year

that is about 43 failed checks a month at a 60-second interval.

the nines, at a glance

uptime	per day	per week	per month	per year
90%	2h 24m	16h 48m	3d	36d 12h
95%	1h 12m	8h 24m	1d 12h	18d 6h
99%	14m 24s	1h 40m 48s	7h 12m	3d 15h 36m
99.5%	7m 12s	50m 24s	3h 36m	1d 19h 48m
99.9%	1m 26s	10m 5s	43m 12s	8h 45m 36s
99.95%	43s	5m 2s	21m 36s	4h 22m 48s
99.99%	8.6s	1m	4m 19s	52m 34s
99.999%	864ms	6s	26s	5m 15s

Month is 30 days, year is 365 days. Day and week are exact.

uptime percentage calculator, in reverse

Know your downtime budget instead? Enter how long you can be down and get the uptime percentage it works out to.

allowed downtime

per

that is 99.8611% uptime

what uptime percentage really means

99.9% uptime allows 43 minutes 12 seconds of downtime per month, or 8 hours 45 minutes per year. Uptime is the share of a period your service answers correctly, and the gap to 100% is your downtime budget. Three nines sounds airtight until you turn it into wall-clock time: it still leaves 43 minutes a month for a bad deploy, an expired certificate or a database that stops answering.

from a number to a budget

Each extra nine costs ten times the effort of the last. Going from 99.9% to 99.99% shrinks your yearly budget from almost nine hours to under an hour, which means retries, health checks and failover have to be automatic, not a person waking up. Pick the target you can measure, then watch it closely enough to defend it.

FAQ

How do you calculate allowed downtime from an uptime percentage?

Multiply the length of the period by one minus the uptime fraction. At 99.9%, a 30-day month allows 30 days times 0.001, which is 43 minutes and 12 seconds of downtime.

How do I calculate an uptime percentage?

Subtract the downtime share from 100%. If a service was down 43 minutes in a 30-day month, uptime is (2,592,000 seconds minus 2,580) divided by 2,592,000, which is about 99.9%. The reverse calculator above turns a downtime figure straight into the percentage.

What is the difference between an SLA and an SLO?

An SLO is the reliability target you set internally, such as 99.9% uptime. An SLA is the contract you sign with a customer, usually a looser number with a refund if you miss it. Both use the same downtime math.

How much downtime does 99.9% allow?

Three nines allows about 8 hours 45 minutes a year, 43 minutes a month, or 1 minute 26 seconds a day. 99.99% cuts that to roughly 52 minutes a year.

What uptime should I aim for?

Most SaaS products commit to 99.9% and run internally toward 99.95%. Chasing a fifth nine is expensive and rarely worth it unless a payment or safety flow depends on it. Pick a number you can actually measure and alert on.

How is the month and year length defined here?

A month is 30 days and a year is 365 days, the convention most SLA tables use. Day and week are exact. Change the percentage and every column recomputes.

A budget you can't see is a budget you'll blow.

Uptimepage checks your endpoints every minute, opens an incident the moment one fails, and shows the whole record on a public status page. Start free, no card.

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