Most hosting providers advertise an uptime figure: the percentage of time your website is expected to be online and reachable. Figures such as 99%, 99.9%, and 99.99% look almost identical at a glance. Converted into time, the differences are significant.
What the percentages mean in hours and minutes
The table below shows the maximum downtime each figure allows over a year and over a 30-day month.
| Uptime | Downtime per year (approx) | Downtime per month (approx) |
|---|---|---|
| 99% | 3.5 days | 7h15m |
| 99.5% | 2 days | 3h30m |
| 99.9% | 8h45m | 45 minutes |
| 99.95% | 4h30m | 20 minutes |
| 99.99% | 50 minutes | 4 minutes |
The step from 99% to 99.9% reduces allowable downtime by a factor of ten: from more than three and a half days a year to under nine hours.
What counts as "downtime"
An uptime guarantee is usually defined in a provider's service level agreement (SLA), and the SLA decides what is measured. Common points to check:
- Scheduled maintenance. Many SLAs exclude planned maintenance from downtime calculations, provided you were notified in advance.
- What is being measured. Some guarantees cover the server or network only. Your website can still be unreachable because of a problem with your site's own code, its database, or its email service, without counting as downtime.
- Causes outside the provider's control. Large-scale internet outages, attacks, and events such as natural disasters are often excluded.
- Who has to notice. Some providers only count downtime that you report and that their own monitoring confirms.
A high percentage with many exclusions can offer less practical protection than a slightly lower percentage with few.
Compensation: what a guarantee usually means
An uptime guarantee is rarely a promise that your site will not go down. More often, it is a promise of compensation if it does. This is typically:
- A credit against future hosting fees, not a cash refund.
- Calculated as a percentage of that month's fee, scaled to how far uptime fell below the guarantee.
- Capped, often at the cost of one month's hosting.
- Only available if you claim it, usually within a set time after the outage.
For most shared hosting plans, the compensation for a significant outage is small compared to the cost to a business of being offline. The guarantee is better read as a signal of the standard the provider aims for than as insurance.
When uptime matters more
For a personal or hobby site, a few hours of downtime a year is usually an inconvenience. For an online store, a booking system, or a site that generates enquiries, downtime can mean lost sales and frustrated customers. Email hosted on the same plan may also be affected during an outage.
If your site is business-critical, a higher uptime figure, a clearly worded SLA, and responsive support all carry more weight. How quickly a provider responds during an outage is covered in Getting Help When You Need It: Why Customer Support Matters More Than It Looks.
Checking a provider's real track record
An advertised figure is a target. To see how a provider has actually performed, you can:
- Look for a public status page that lists past incidents and how long they lasted.
- Search for independent reports or discussions of outages.
- Ask the provider for their measured uptime over the past 12 months.
- Use a free external uptime monitoring service on your own site once it is live, so you have your own record.
Advertised uptime figures are also worth noting when comparing web hosts. Uptime is one of several factors to weigh together, and it appears alongside pricing and features in A Practical Checklist for Comparing Hosting Providers Side by Side.
*This article was drafted with the help of AI. It was fact-checked and edited by a real person.