Uptime percentages are easier to compare as time. The gap between the figures is larger than it looks written as decimals.

  • 99% - 7 hours 18 minutes a month.
  • 99.9% - 43 minutes a month.
  • 99.99% - 4 minutes 23 seconds a month.
  • 99.999% - 26 seconds a month, which means no human is in the recovery path.

What an SLA measures

Almost always the availability of the SERVICE - the machine responding, the network reachable. It does not usually cover your application returning 500, and it never covers a mistake in your own code or a plugin update that broke the site.

Planned maintenance is usually excluded

Most agreements exclude announced maintenance windows from the calculation. A provider can be down for two hours a month and still report 100%, entirely honestly, because the window was announced.

What the credit is worth

An SLA breach normally returns a percentage of the monthly fee as credit. On a small plan that is a few pounds. It is a statement of confidence, not insurance - if downtime costs you more than the fee, the SLA is not the protection you need.

Measure it yourself

Check from outside, for a string on the page rather than a status code, from more than one location - so that one failing monitor does not read as an outage.

curl -fsS --max-time 10 https://yourdomain.com/ | grep -q 'Sign in' || echo DOWN
Ask how it is measured and what is excluded before comparing two numbers. Two providers can both say 99.9% and mean genuinely different things.