SLA & Uptime Calculator
Turn any uptime percentage into the downtime it actually allows — per day, week, month, and year — and work backward from real downtime to the SLA you hit.
Enter any value, e.g. 99.95.
Allowed downtime
Three nines- / day
- 1m 26.4s
- / week
- 10m 4.8s
- / month basis
- 43m 50s
- / quarter
- 2h 11m 30s
- / year
- 8h 45m 36s
That's your error budget — the downtime your SLO permits before you breach. How to defend it →
Reference
Uptime to downtime: the reference table
The canonical lookup, as real semantic HTML — copy it, deep-link any row, or click a row to load it into the calculator.
| Uptime % | Common name | / day | / week | / month | / quarter | / year |
|---|---|---|---|---|---|---|
| 90%# | One nine | 2h 24m | 16h 48m | 3d 1h 3m 21.6s | 9d 3h 10m 4.8s | 36d 12h |
| 95%# | — | 1h 12m | 8h 24m | 1d 12h 31m 40.8s | 4d 13h 35m 2.4s | 18d 6h |
| 98%# | — | 28m 48s | 3h 21m 36s | 14h 36m 40.3s | 1d 19h 50m 1s | 7d 7h 12m |
| 99%# | Two nines | 14m 24s | 1h 40m 48s | 7h 18m 20.2s | 21h 55m 0.5s | 3d 15h 36m |
| 99.5%# | — | 7m 12s | 50m 24s | 3h 39m 10.1s | 10h 57m 30.2s | 1d 19h 48m |
| 99.9%# | Three nines | 1m 26.4s | 10m 4.8s | 43m 50s | 2h 11m 30s | 8h 45m 36s |
| 99.95%# | — | 43.2s | 5m 2.4s | 21m 55s | 1h 5m 45s | 4h 22m 48s |
| 99.99%# | Four nines | 8.6s | 1m 0.5s | 4m 23s | 13m 9s | 52m 33.6s |
| 99.999%# | Five nines | 0.9s | 6s | 26.3s | 1m 18.9s | 5m 15.4s |
Downtime is calculated on a 30.44-day average calendar month (365 ÷ 12). A flat 30-day month gives slightly smaller figures — e.g. 99.9% = 43m 12s instead of 43m 50s. We disclose the basis because most calculators don't.
What the nines actually mean
Each extra nine cuts the allowed downtime by roughly 10× — and usually means a large step in engineering cost. The jump from 99.9% (about 44 minutes/month) to 99.99% (about 4 minutes/month) typically buys you redundancy, automated failover, and sub-minute detection. The next step, 99.999% ("five nines"), leaves you only about 26 seconds of downtime a month — territory where humans can't react fast enough and everything has to be automated. Whether that last fraction of a percent is worth it depends entirely on what an outage actually costs you.
SLA vs SLO vs SLI — and your error budget
An SLI is the measured signal — for example, the percentage of successful requests. An SLO is your internal target for that signal. An SLA is the contractual promise you make to customers, usually looser than the SLO so you have headroom before a breach has financial consequences. Your error budget is what's left over: 100% minus your target. You monitor the SLI, manage to the SLO, and report against the SLA. See how uptime monitoring fits in →
How we calculate this
The core formula is downtime = (1 − uptime ÷ 100) × periodSeconds. We use a 30.44-day average calendar month (365 ÷ 12 = 30.4375), a 365-day year, a 7-day week, and a quarter of 3 average months (91.32 days). Seconds are shown to one decimal place, and whole units with a zero value are dropped (so 90% over a week reads "16h 48m", not "0d 16h 48m 0s"). Leap years add a day to the calendar but we report the long-run average so the yearly figure stays stable. We disclose the month basis because it changes the headline number and most calculators don't.
FAQ
Frequently asked questions
99.9% ("three nines") allows about 43 minutes 50 seconds of downtime per average (30.44-day) month — roughly 8 hours 45 minutes per year. Every extra nine cuts the allowed downtime by about 10×.
99.9% allows about 43m 50s/month; 99.99% ("four nines") allows only about 4m 23s/month. That 10× tighter budget usually means redundancy, automated failover, and sub-minute detection — a large jump in engineering cost for the last 0.09%.
Your error budget is the downtime your SLO permits — 100% minus your target. At a 99.9% SLO you have a 0.1% error budget (about 43m 50s/month) to spend on incidents, risky deploys, and maintenance before you breach.
An SLI is the measured signal (e.g. % of successful requests). An SLO is your internal target for it. An SLA is the contractual promise to customers — usually looser than the SLO — with penalties if you miss it. You monitor the SLI, manage to the SLO, and report against the SLA.
Uptime % = (total time − downtime) ÷ total time × 100, over a defined window. The window matters: 5 minutes of downtime is 99.99% over a month but only 99.65% over a single day. Always state the measurement period alongside the number.
We use a 30.44-day average calendar month (365 ÷ 12), which matches how most SLAs and the widely-cited reference tools report monthly downtime. A flat 30-day month gives slightly smaller figures (99.9% = 43m 12s vs 43m 50s). The yearly figure uses 365 days.
From SLA target to SLA defended
A downtime budget is only as good as how fast you spot a breach.
Drumbeats watches your sites, APIs, and jobs with sub-minute checks and alerts the moment you start spending your error budget — before it turns into a missed SLA.
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