Free website tool
Uptime and SLA Calculator
Turn an SLA percentage like 99.9% into allowed downtime per day, week, month and year, or work out uptime from downtime.
%
Daily
1m 26.4s
allowed downtime
Weekly
10m 4.8s
allowed downtime
Monthly
43m 49.7s
allowed downtime
Quarterly
2h 11m 29s
allowed downtime
Yearly
8h 45m 57s
allowed downtime
Common SLA levels
| Uptime | Daily | Weekly | Monthly | Quarterly | Yearly |
|---|---|---|---|---|---|
| 90% | 2h 24m | 16h 48m | 3d 1h 2m | 9d 3h 8m | 36d 12h 34m |
| 95% | 1h 12m | 8h 24m | 1d 12h 31m | 4d 13h 34m | 18d 6h 17m |
| 99% | 14m 24s | 1h 40m 48s | 7h 18m 17s | 21h 54m 52s | 3d 15h 39m |
| 99.5% | 7m 12s | 50m 24s | 3h 39m 9s | 10h 57m 26s | 1d 19h 49m |
| 99.9% | 1m 26.4s | 10m 4.8s | 43m 49.7s | 2h 11m 29s | 8h 45m 57s |
| 99.95% | 43.2s | 5m 2.4s | 21m 54.9s | 1h 5m 45s | 4h 22m 58s |
| 99.99% | 8.64s | 1m 0.5s | 4m 23s | 13m 8.9s | 52m 35.7s |
| 99.999% | 864ms | 6.05s | 26.3s | 1m 18.9s | 5m 15.6s |
How the numbers are calculated
Allowed downtime is simply the period length multiplied by the share of time the service may be down: (100% − SLA) × period. A year is 365.2425 days, the Gregorian average, and a month is a twelfth of that (30.44 days), so monthly figures are an average; a 31-day month allows slightly more.
- SLA → downtime: what a promise like 99.95% means in minutes.
- Downtime → SLA: what last month’s 45-minute outage did to your uptime.
- Combined SLA: the real availability of several services together, in series or redundant.
Everything is calculated in your browser.
Frequently asked questions
- How much downtime does 99.9% uptime allow?
- About 1 minute 26 seconds a day, 10 minutes a week, 43 minutes 50 seconds a month and 8 hours 46 minutes a year. Each extra nine cuts that by ten: 99.99% allows about 4 minutes 23 seconds a month, and 99.999% (“five nines”) about 26 seconds.
- Does scheduled maintenance count as downtime?
- It depends on the contract. Many hosting and cloud SLAs exclude announced maintenance windows, and most measure per calendar month, with credits paid only if you claim them. Read how the provider defines “unavailable”: some count only full outages, others count error rates above a threshold.
- How do I calculate the uptime of a whole website stack?
- When every part must work (DNS, CDN, server, database), multiply their availabilities: three services at 99.9% each give about 99.7% together, so the whole is always less reliable than its weakest part. Redundancy works the other way: two independent copies at 99% each, where one is enough, give 99.99%. The Combined SLA tab does both.