Uptime · downtime budget · composite SLA
SLA & Uptime Calculator
Turn an SLA percentage into allowed downtime per day, week, month and year, find the SLA a downtime budget requires, and combine dependent or redundant services into one end-to-end figure.
Target uptime
Allowed downtime is (1 − uptime) × period, based on a 365.25-day year (so a month is 30.44 days). Most SLAs measure monthly.
Allowed downtime at 99.9%
Per day
1m 26s
Per week
10m 5s
Per month
43m 50s
Per quarter
2h 11m
Per year
8h 45m
The nines: allowed downtime reference
Maximum downtime each SLA tier permits per period.
| SLA | day | week | month | quarter | year |
|---|---|---|---|---|---|
| 90% | 2h 23m | 16h 47m | 3d 1h | 9d 3h | 36d 12h |
| 95% | 1h 12m | 8h 24m | 1d 12h | 4d 13h | 18d 6h |
| 98% | 28m 48s | 3h 21m | 14h 36m | 1d 19h | 7d 7h |
| 99% | 14m 24s | 1h 40m | 7h 18m | 21h 54m | 3d 15h |
| 99.5% | 7m 12s | 50m 24s | 3h 39m | 10h 57m | 1d 19h |
| 99.9% | 1m 26s | 10m 5s | 43m 50s | 2h 11m | 8h 45m |
| 99.95% | 43.2s | 5m 2s | 21m 55s | 1h 5m | 4h 22m |
| 99.99% | 8.6s | 1m | 4m 23s | 13m 9s | 52m 36s |
| 99.999% | 864 ms | 6s | 26.3s | 1m 19s | 5m 16s |
| 99.9999% | 86 ms | 605 ms | 2.6s | 7.9s | 31.6s |
About this tool
This SLA and uptime calculator turns a service-level percentage into the downtime it actually allows. Enter a figure like 99.9% or 99.99% and see the maximum permitted outage per day, week, month, quarter and year at a glance — the numbers you need when you negotiate a contract, set an error budget, or sanity-check a vendor promise.
It goes further than a simple converter. A reverse mode works back from a downtime budget ("we can tolerate one hour a month") to the SLA percentage that implies, and a composite mode combines several services into one end-to-end figure: chain dependent components (every one must be up, so availability multiplies) or model redundant ones (the system stays up if any survive). A reference table lists every common "nine" so you can compare tiers instantly.
Everything runs in your browser with nothing uploaded. Calculations use a 365.25-day year, which makes a month 30.44 days and lines up with the canonical reference values (99.9% is 8.77 hours a year, or 43.83 minutes a month).
Frequently asked questions
What does 99.9% uptime mean in real downtime?+
At 99.9% ("three nines") a service may be down about 8.77 hours per year, 43.83 minutes per month, 10.1 minutes per week or 1.44 minutes per day. The calculator shows all of these as soon as you type the percentage.
What is the difference between 99.9% and 99.99%?+
Each extra nine cuts the allowed downtime by roughly ten times. 99.9% permits about 43.8 minutes of downtime per month; 99.99% ("four nines") permits only about 4.38 minutes; 99.999% ("five nines") about 26 seconds.
How do I combine the SLAs of services my app depends on?+
Use the composite mode. For dependent services where every one must be up (a load balancer, then an app server, then a database), availability is the product of each SLA, so the combined figure is always lower than the weakest link. For redundant services where any one staying up is enough, the calculator multiplies the failure rates instead, so adding redundancy raises the total.
How is a month defined in the calculation?+
A month is one twelfth of a 365.25-day year, i.e. 30.44 days, which matches the figures most uptime references quote. Some contracts instead use a flat 30-day month or the actual calendar month, which shifts the monthly downtime slightly — always check how your specific SLA defines the measurement window.
Does planned maintenance count against the SLA?+
It depends on the agreement. Many SLAs exclude scheduled maintenance windows that are announced in advance and only count unplanned outages, so the real budget can be larger than the raw percentage suggests. Read the definitions and exclusions in your contract before relying on a number.