SLA Calculator

Turn an uptime percentage into allowed downtime, convert downtime back to uptime, or find exactly when a support ticket is due under a business-hours SLA. Free, no sign-up.

What kind of SLA?
Calculate
%
Allowed downtime at 99.9% uptime
Daily
1m 26.4s
Weekly
10m 4.8s
Monthly
43m 49.8s
Quarterly
2h 11m 29.4s
Yearly
8h 45m 57.6s

Uses a 365.25-day year, so a month is 30.44 days and a quarter is 91.31 days on average.

Free. No sign-up. Everything is calculated in your browser, nothing you enter is sent anywhere.

How it's calculated

Allowed downtime
Downtime = period length x (1 - uptime % / 100)
Uptime from downtime
Uptime % = (1 - downtime / period length) x 100
Period lengths
Day 24h Week 7d Month 30.44d Quarter 91.31d Year 365.25d
Response due time
Due = received time + target, counting only business days and hours
Worked examples

SLA calculation examples

Common uptime targets and a response-time SLA that runs over a weekend.

Three nines

A standard 99.9% uptime commitment.

Uptime target 99.9%.

0.1% of the time can be down: 1m 26s a day, 43m 50s a month, or 8h 46m a year.

Four nines

A premium tier promising 99.99%.

Uptime target 99.99%.

Only 4m 23s of downtime a month, or 52m 36s a year. One slow deploy can use the whole monthly budget.

Downtime to uptime

An incident took the service down for 45 minutes this month.

45 minutes of downtime per month.

1 - 2,700 / 2,629,800 seconds gives 99.897% uptime for the month. That misses a 99.9% SLA.

Response SLA over a weekend

A 4 business hour first response target, Monday to Friday, 9:00 to 17:00.

Ticket received Friday at 15:00.

Two business hours run out Friday at 17:00. The clock pauses for the weekend and the last two hours run Monday 9:00 to 11:00, so the reply is due Monday at 11:00.

Writing a good SLA

What to decide before you commit to a number

The math is simple. The definitions around it are where most SLA disputes start.

01

Each extra nine cuts downtime tenfold

99% allows about 7 hours 18 minutes a month, 99.9% about 44 minutes, 99.99% about 4 minutes. Cost and effort rise sharply with each nine.

02

Define the measurement window

A monthly SLA resets every month, a yearly one lets a bad month be offset. State the period, and whether planned maintenance counts, in the agreement.

03

Response SLAs should say business or calendar hours

"4 hours" means very different things at 16:00 on a Friday. Spell out your business hours, days and timezone, and how holidays are handled.

04

Measure first response, not resolution, unless you mean it

Most support SLAs promise a first reply time. Resolution time depends on the problem and is harder to guarantee, so it usually gets a separate, looser target.

FAQ

Questions people ask

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