Uptime Calculator (SLA Downtime)
Turn an SLA percentage into allowed downtime per day, week, month, quarter and year, get uptime from observed downtime, and combine services in series or parallel.
Check how your SLA defines a month and which events (maintenance windows, partial outages) count as downtime.
| Availability | 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 |
| 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% | 9s | 1m | 4m 19s | 52m 34s |
| 99.999% | 864 ms | 6s | 26s | 5m 15s |
| 99.9999% | 86 ms | 605 ms | 3s | 32s |
Service level agreements promise availability as a percentage — 99.9%, 99.99% — which hides how much downtime that really allows. This calculator converts any SLA into allowed downtime per day, week, month, quarter and year, turns observed outage minutes into an uptime percentage and "number of nines", and works out the combined availability of components in series or in parallel. A table lists the usual nines from 90% to 99.9999%.
How to use this tool
- Choose what to calculate.
- For an SLA, enter the percentage and the month and year lengths your contract uses.
- For observed uptime, enter the total downtime and the period.
- For a system, list the availabilities of its parts and say whether they are in series or redundant.
Formula
downtime = (1 − A) × period · uptime = (period − downtime) ÷ period · series A = A₁ × A₂ × … · parallel A = 1 − (1 − A₁)(1 − A₂)…
A is availability as a fraction (99.9% = 0.999). Contracts differ on the month: a 30-day month gives 43,200 minutes, the average month 30.44 days. Number of nines = −log₁₀(1 − A).
Example
99.9% ("three nines") allows 0.001 × 8,760 h = 8.76 hours a year (8 h 45 min 36 s) or 43.2 minutes in a 30-day month. 99.99% allows only 4.32 minutes a month. Two services of 99.9% each give 99.8001% when both are needed, but 99.9999% when either one is enough.
Frequently asked questions
Is 99.9% good?
It is a common SLA for business software, allowing about 43 minutes of downtime a month. Critical infrastructure aims for 99.99% or more, which leaves little room for maintenance without redundancy.
Does planned maintenance count?
It depends on the contract. Many SLAs exclude announced maintenance windows; check the definitions section.
Why is my system less available than any single part?
In series every part must work, so the availabilities multiply. Five parts at 99.9% give about 99.5% in total.
Last updated:
Page address with these inputs: https://kakao.mobile/tools/uptime-calculator/
Cite or embed this tool
kakaoCalc. (2026, November 8). Uptime Calculator (SLA Downtime). https://kakao.mobile/tools/uptime-calculator/
“Uptime Calculator (SLA Downtime).” kakaoCalc, 8 Nov. 2026, kakao.mobile/tools/uptime-calculator/.
Paste this code into your page. The widget runs in your visitors' browsers, shows no ads and keeps a link back to this page. Embedding terms