Uptime is the percentage of time a website or server is up and reachable.
Uptime is the share of time a website or server is online and responding to visitors, written as a percentage. A host with 99.9% uptime over a 30-day month had your site reachable for all but about 43 minutes of that month. The opposite is downtime, the time it wasn't.
Uptime sounds like a simple yes or no, but it depends on what's measured. A server can be switched on while the website on it returns errors, so good monitoring checks that real pages load, not just that the machine answers a ping.
How uptime is measured
Monitoring services send a request to your site every minute or so, often from several locations. If the site doesn't respond, or responds with an error, after a few retries, that time is recorded as down. Uptime is then the total time minus the downtime, divided by the total time and shown as a percentage.
What uptime percentages mean in practice
- 99%: about 7 hours 12 minutes of downtime a month, or more than 3.5 days a year
- 99.9%: about 43 minutes a month, or nearly 9 hours a year
- 99.95%: about 22 minutes a month
- 99.99%: about 4 minutes a month, or under an hour a year
Each extra nine is much harder for a host to deliver, because it needs more redundant hardware, power and networking.
Why uptime matters for your website
When your site is down, visitors can't buy, book or contact you, and many won't try again. Search engines that hit your site during a long outage may crawl it less often, and repeated outages can hurt rankings.
What causes downtime
- Hardware or network failures at the data centre
- Scheduled maintenance and software updates
- Traffic spikes or attacks that overwhelm the server
- Problems in your own site, like a broken plugin or a full storage quota
- An expired domain or misconfigured DNS
Some of these are the host's responsibility and some are yours, which is why uptime promises usually come with exclusions.
Uptime guarantees and SLAs
An uptime guarantee is normally written into an SLA, which says what you get if the host misses the target. AblePage offers a 99.9% uptime SLA with account credit on every plan, and scheduled maintenance is excluded from SLA credits.
How to monitor your own uptime
Use an external monitoring service that checks your site every few minutes and alerts you by email or text. Monitor the page that matters most, such as your shop or login, rather than just the home page, and keep an eye on your domain's expiration date too.