Uptime and SLA Downtime Calculator
Enter an SLA uptime percentage (such as 99.9%) to see how much downtime is allowed. You can also work backward from the downtime to the uptime.
How the allowed downtime is calculated
- Allowed downtime = period × (100 − uptime) ÷ 100
- Uptime (%) = (period − downtime) ÷ period × 100
The calculation uses fractions, so there is no decimal rounding error. Seconds are rounded to 3 decimal places and shown as days, hours, minutes and seconds. You can enter the uptime with up to 6 decimal places, and the result shows enough digits that a value close to 0% or 100% is not displayed as 0% or 100%.
Choosing the period
- 1 day: 24 hours (86,400 seconds)
- 1 week: 7 days
- 1 month: choose 28, 29, 30 or 31 days. The default is 30 days. Because the allowed downtime changes with the number of days (a 31-day month allows more than a 30-day month), the result shows the period that was used.
- 1 year: 365 days, or 366 days in a leap year
- Enter the number of days: 1 to 3,660 days
Examples
| Uptime | 1 day | 30-day month | 365-day year |
|---|---|---|---|
| 99% | 14 min 24 s | 7 h 12 min | 3 d 15 h 36 min |
| 99.9% | 1 min 26.4 s | 43 min 12 s | 8 h 45 min 36 s |
| 99.99% | 8.64 s | 4 min 19.2 s | 52 min 33.6 s |
| 99.999% | 0.864 s | 25.92 s | 5 min 15.36 s |
- 99.9% in a 31-day month: 44 min 38.4 s. In a 28-day month: 40 min 19.2 s.
- Working backward: if a service is down for 43 min 12 s in a 30-day month, its uptime is 99.9%.
Points to check in a contract
The uptime percentage in an SLA is defined differently from contract to contract. Do not compare the numbers alone; check the definitions in the contract.
- The time that is measured: 24/7, or business hours only
- Exclusions: whether planned maintenance, causes on the customer's side or force majeure count as downtime
- The definition of an outage: only a complete outage, or also a high error rate or slow responses
- Measurement interval and rounding: per minute, per 5 minutes, and so on
- What happens when the target is missed: refunds, service credits and so on
This calculator gives the result of a simple division. It does not show any guarantee or compensation in a contract.
Things to know
- The uptime is a number from 0 to 100 (up to 6 decimal places). For 100%, the allowed downtime is 0; for 0%, it is the whole period.
- If the downtime is longer than the period, an error is shown.
- To convert between seconds, minutes and hours, use the Time Converter. For the cron schedule of a recurring job, use the Cron Expression Calculator.
Frequently asked questions
How many minutes of downtime does 99.9% allow per month?
43 min 12 s in a 30-day month, 44 min 38.4 s in a 31-day month, and 40 min 19.2 s in a 28-day month.
What are "five nines"?
An uptime of 99.999%. In a 365-day year, the allowed downtime is 5 min 15.36 s.
How much does the allowed downtime shrink with each extra nine?
Each additional 9 divides the allowed downtime by 10 (99% to 99.9% is one tenth).