Uptime percentages explained: what 99.9% really means
"Three nines" sounds nearly perfect, but the difference between 99% and 99.99% is the difference between days of downtime a year and under an hour.
The table
Uptime is the share of time a site is reachable. Everything else follows from arithmetic — here is how much downtime each target allows:
| Uptime | Per day | Per week | Per month | Per year |
|---|---|---|---|---|
| 99% | 14.4 minutes | 1.7 hours | 7.3 hours | 3.7 days |
| 99.5% | 7.2 minutes | 50.4 minutes | 3.7 hours | 1.8 days |
| 99.9% | 1.4 minutes | 10.1 minutes | 43.8 minutes | 8.8 hours |
| 99.95% | 43 seconds | 5.0 minutes | 21.9 minutes | 4.4 hours |
| 99.99% | 9 seconds | 1.0 minutes | 4.4 minutes | 52.6 minutes |
Each extra nine cuts allowed downtime by a factor of ten — and costs far more to achieve. Going from 99% to 99.9% usually means better hosting and monitoring. Going from 99.9% to 99.99% usually means redundant infrastructure.
Which target is realistic?
- 99% — about 7 hours a month. Acceptable for a hobby site, not for a business that takes bookings or orders.
- 99.9% — about 43 minutes a month. A sensible target for a small business website on decent hosting.
- 99.99% — about 4 minutes a month. Needs redundancy; realistic for larger services with engineering teams.
How uptime is measured matters
- Check interval. A 5-minute monitor can't see a 2-minute outage precisely; it estimates from the checks that failed.
- Confirmation. A single failed check that immediately recovers is a blip, not an outage. Honest reports count only confirmed outages.
- Planned maintenance. Most SLAs — and OwlHound — exclude scheduled windows.
- Rounding. Real downtime should never be rounded up to a flattering 100%.
OwlHound calculates uptime from confirmed outages and shows it on your dashboard, weekly report and public status page.
Frequently asked questions
What is a good uptime percentage?
For a small business website, 99.9% (about 43 minutes of downtime a month) is a sensible target and what many hosts advertise. Most small sites on decent hosting land between 99.9% and 99.99% in practice.
Does maintenance count as downtime?
Under many SLAs, planned maintenance is excluded. In OwlHound, time inside a scheduled maintenance window is not counted against your uptime.
Why does my host's uptime differ from my monitor's?
Hosts usually measure their own infrastructure from inside the network. An external monitor also catches DNS problems, certificate failures and routing issues the host doesn't count.
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