What is uptime?
By Ash, Founder, HosteazePublished 2 min read
The short answer
Uptime is the percentage of time a website or server is online and responding. Hosts usually quote it as a target such as 99.9%, which still allows about 8 hours 46 minutes of downtime a year, or roughly 43 minutes a month. The extra nines matter more than they look, so read the small print.
Uptime sounds like a boring number on a hosting sales page until your site goes down on the Saturday morning you sent out a newsletter. It's simply how much of the time your website is reachable and working, written as a percentage. The opposite, downtime, is what you're really trying to measure.
What does 99.9% uptime mean in hours?
Percentages near 100 all look alike, so convert them into time. Here's what each common figure allows, based on a 365-day year and a 30-day month.
| Uptime | Downtime per year | Downtime per month |
|---|---|---|
| 99% | about 3 days 16 hours | about 7 hours 12 minutes |
| 99.5% | about 1 day 20 hours | about 3 hours 36 minutes |
| 99.9% | about 8 hours 46 minutes | about 43 minutes |
| 99.99% | about 53 minutes | about 4 minutes |
The jump from 99% to 99.9% is the difference between more than three and a half days offline and one bad evening. For a small business site, 99.9% is a sensible bar. Hosteaze works to a 99.9% uptime target on UK servers.
How is uptime measured?
Usually by a monitoring service that requests your site every minute or few minutes from several locations. If it gets no answer, or a server error such as a 500 internal server error or 503 error, the clock starts on downtime.
Two catches. A host's figure normally covers its servers, not your site's code, so a broken plugin that takes WordPress down won't count against them. And the measurement interval matters: checking every five minutes can miss short outages entirely.
How can I check my own site's uptime?
- Sign up for a free uptime monitoring service. Several offer free plans that check every few minutes.
- Add your homepage address, including
https://. - Add a second check for a page that uses your database, such as a blog post, so you catch database failures too.
- Set alerts to go to your phone, not just an inbox you check once a day.
- Review the monthly report and compare it with what your host promises.
If your own monitoring keeps showing more downtime than your host's target allows, that's one of the clearest signs you need to switch web hosts.
More plain-English guides are in Email and domains.
Frequently asked questions
Does planned maintenance count as downtime?
It depends on the host. Many exclude scheduled maintenance from their uptime figure as long as they warn you in advance. Check the terms, because a lot of maintenance can hide behind a good-looking percentage.
What's the difference between an uptime target and an uptime guarantee?
A target is what the host aims for. A guarantee, usually written into a service level agreement (SLA), promises something back, normally service credits, if they miss it. Credits rarely cover what an outage costs you, so treat either as a signal of how seriously the host takes reliability.
Does downtime hurt my Google rankings?
A short outage won't. Google slows its crawling when it sees server errors and keeps already indexed pages for a while, but pages that keep returning server errors are eventually dropped from the index.