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Convert an uptime percentage into real downtime
See exactly how much downtime a given uptime guarantee actually allows, per day, week, month, and year.
Figures use a 365.25-day year and a 30.44-day month.
99% uptime allows up to 3d 15h 39m 36s of downtime per year.
Hosting providers often advertise an uptime guarantee, like 99.9% uptime, as part of their service level agreement (SLA). That number is easy to skim past, but the actual amount of downtime it allows varies a lot depending on the time period you're looking at. This tool converts an uptime percentage into concrete downtime figures so you can judge what a guarantee really means.
Enter an uptime percentage, or pick one of the common SLA levels, and the calculator shows the equivalent downtime per day, week, month, and year. Use it to sanity-check a provider's advertised SLA, or to compare two providers' guarantees on equal footing.
Here's how several common uptime guarantees translate into downtime, based on a 365.25-day year and a 30.44-day average month:
| Uptime | Downtime / Day | Downtime / Week | Downtime / Month | Downtime / Year |
|---|---|---|---|---|
| 99% | 14m 24s | 1h 40m 48s | 7h 18m 17s | 3d 15h 39m |
| 99.5% | 7m 12s | 50m 24s | 3h 39m 8s | 1d 19h 50m |
| 99.9% | 1m 26s | 10m 5s | 43m 50s | 8h 45m 58s |
| 99.95% | 43s | 5m 2s | 21m 55s | 4h 22m 59s |
| 99.99% | ~9s | 1m 0s | 4m 23s | 52m 36s |
| 99.999% | ~1s | 6s | 26s | 5m 16s |
A 99.9% uptime guarantee sounds close to perfect, and over a year it's still under nine hours of allowed downtime. But if that downtime happens to land in one stretch, it could mean your site is unreachable for the better part of an hour in a single incident and still leave the provider technically within its SLA for the month. Uptime percentages describe an average over the full period, not a promise about how downtime is distributed.
Providers usually calculate uptime by monitoring their servers or network at regular intervals and recording the percentage of checks that succeeded over a billing period. Methodology can vary — some providers exclude scheduled maintenance windows from downtime calculations, while others count all downtime regardless of cause. When an SLA matters to you, it's worth checking a provider's specific terms for how they define and measure downtime, and whether missing the guarantee results in service credits.
An SLA is a target and, often, a basis for service credits if it's missed — it's not a guarantee that outages won't happen. When comparing providers, it's worth looking at both the advertised uptime figure and what customers actually report in reviews. Our Hosting Horizon Score Reliability criterion reflects reviewer-reported experience, which can be a useful complement to a provider's official SLA number.
If you're trying to figure out whether a specific site is down at this moment rather than calculating a theoretical SLA, use our Is It Down or Just Me? tool instead.
It depends on the provider’s specific terms. Most SLAs count time when your service is unreachable due to the provider’s infrastructure, though some exclude scheduled maintenance. Check a provider’s SLA terms for its exact definition.
99.9% is a common and generally solid guarantee for most sites, allowing under nine hours of downtime a year. Higher guarantees like 99.99% allow far less, but the difference may matter more for high-traffic or business-critical sites.
This calculator only converts a percentage into downtime figures; it doesn’t track whether any specific provider meets its SLA. Reviewer feedback on a provider’s Hosting Horizon Score Reliability criterion can offer a sense of real-world experience.
Many providers offer service credits or account credit if uptime falls below the guaranteed level in a billing period, but the specifics vary. Check the provider’s own SLA terms for details.
Using 365.25 days accounts for leap years, giving a more accurate long-term average than a flat 365-day year.
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