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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.

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
98% 28m 48s 3h 21m 36s 14h 24m 7d 7h 12m
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

downtime by SLA level

Downtime allowed at 98%

A 98% SLA allows 28m 48s of downtime per day, 3h 21m 36s per week, 14h 24m per month and 7d 7h 12m per year.

Fine for an internal tool or a staging box. In a contract it reads as more than fourteen hours of monthly downtime, which is a hard sell.

The full guide to 98% uptime

Downtime allowed at 99%

A 99% SLA allows 14m 24s of downtime per day, 1h 40m 48s per week, 7h 12m per month and 3d 15h 36m per year.

Two nines. Almost a full working day of downtime every month, and most of it tends to arrive in business hours.

Downtime allowed at 99.5%

A 99.5% SLA allows 7m 12s of downtime per day, 50m 24s per week, 3h 36m per month and 1d 19h 48m per year.

Where single-server setups without failover usually land. A weekly maintenance window still fits, barely.

Downtime allowed at 99.9%

A 99.9% SLA allows 1m 26s of downtime per day, 10m 5s per week, 43m 12s per month and 8h 45m 36s per year.

Three nines, the most common SaaS commitment. One bad deploy a month can eat the whole budget.

The full guide to 99.9% uptime

Downtime allowed at 99.95%

A 99.95% SLA allows 43s of downtime per day, 5m 2s per week, 21m 36s per month and 4h 22m 48s per year.

The usual internal target behind a 99.9% contract. It leaves room for one short incident a month, not two.

The full guide to 99.95% uptime

Downtime allowed at 99.99%

A 99.99% SLA allows 8.6s of downtime per day, 1m per week, 4m 19s per month and 52m 34s per year.

Four nines. No human pages fast enough for this; recovery has to be automatic before anyone reads the alert.

The full guide to 99.99% uptime

Downtime allowed at 99.999%

A 99.999% SLA allows 864ms of downtime per day, 6s per week, 26s per month and 5m 15s per year.

Five nines is telecom territory. Five minutes a year needs redundant everything, and few web products earn back what that costs.

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. The contract side is a separate question: what an uptime SLA promises, and what a service credit is actually worth.

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.

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