Website uptime: how much downtime is 99.9%?
Last updated: 9 November 2026
An uptime percentage feels abstract. Convert it into minutes of downtime and the difference becomes clear: 99% and 99.9% are not in the same category.
The table
| Uptime | Downtime per month (30 days) | Downtime per year |
|---|---|---|
| 99% | 7 h 12 | 3 d 15 h |
| 99.5% | 3 h 36 | 1 d 19 h |
| 99.9% | 43 min | 8 h 46 |
| 99.95% | 22 min | 4 h 23 |
| 99.99% | 4 min 19 s | 52 min 36 s |
The calculation: (1 − uptime) × minutes in the period. A 30-day month has 43,200 minutes, so 0.1% of downtime is 43.2 minutes.
Which commitment to choose for a client?
For a brochure site on decent hosting, 99.5% to 99.9% is achievable. 99.99% needs redundant infrastructure: do not promise it on a single server.
What matters most is how it is measured. Monitoring that checks every minute from the outside gives a figure you can show and defend. See the maintenance contract.
Planned or not
Announced maintenance is not an outage. Say in the contract whether it counts or not, and keep the same rules from one month to the next.