# What is Uptime?

> Uptime is the proportion of time a website is online and working, usually given as a percentage such as 99.9%.

- Source: https://nerdsharks.com/glossary/uptime
- Publisher: Nerdsharks (Exeter, Devon, UK)
- Updated: 2026-09-26

Also called: availability, downtime, uptime monitoring, SLA.

Uptime measures how reliably your website is available. Hosting companies often promise a figure like 99.9%, which sounds perfect but still allows nearly nine hours offline across a year.

The opposite is downtime. It can be caused by server problems, expired domains or certificates, hacked sites, or someone changing a setting they should not have.

Uptime monitoring services check your site every few minutes and alert someone when it goes down, so it gets fixed before customers notice.

## Why it matters for a small business

If your website is down when a customer looks you up, they do not wait; they go to the next result. Worse, you will often have no idea it happened. Someone should be watching, and it should not be you finding out from a customer.

**Example:** A landscaper's site goes down on a Friday evening after a hosting fault. An uptime monitor alerts the web developer within minutes, and it is back up before most people would ever notice.