Uptime calculator
An uptime percentage sounds abstract until it's minutes. This converts any SLA number into the downtime it actually permits — per day, week, month, and year.
- per day
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- per week
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- per month
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- per year
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How much downtime does each uptime level allow?
The table below is the whole answer, computed from a 365.25-day year (month = 30.44 days). A service meeting 99.9% ("three nines") can be down for at most 8 hours 46 minutes across a year — or 1 minute 26 seconds in any given day, if the budget is spent evenly.
| Uptime | Downtime / day | / week | / month | / year |
|---|---|---|---|---|
| 90% | 2h 24m | 16h 48m | 3d 1h | 36d 13h |
| 95% | 1h 12m | 8h 24m | 1d 13h | 18d 6h |
| 98% | 28m 48s | 3h 22m | 14h 37m | 7d 7h |
| 99% · two nines | 14m 24s | 1h 41m | 7h 18m | 3d 16h |
| 99.5% | 7m 12s | 50m 24s | 3h 39m | 1d 20h |
| 99.9% · three nines | 1m 26s | 10m 5s | 43m 50s | 8h 46m |
| 99.95% | 43s | 5m 2s | 21m 55s | 4h 23m |
| 99.99% · four nines | 9s | 1m | 4m 23s | 52m 36s |
| 99.999% · five nines | 1s | 6s | 26s | 5m 16s |
How is allowed downtime calculated?
downtime = period × (1 − uptime ⁄ 100). For 99.9% over a 30.44-day month: 730.5 hours × 0.001 = 43.8 minutes. The only judgment call is the calendar convention — this page uses a 365.25-day year and defines a month as one twelfth of it, which is why vendors' tables sometimes differ by a few seconds.
What uptime should you aim for?
Each extra nine costs roughly ten times more than the last, so the honest question is what an hour of downtime costs you. A side project is fine at 99.5%. A store or an API that customers build on usually wants 99.9% or better — and at that level you can't rely on noticing outages yourself, because your entire yearly budget fits inside one night's sleep.
Whatever the target, you can't manage a budget you don't measure.YoPingMe watches your site from three regions, free — and tells you the moment the budget starts burning.