What does 99.9% uptime actually mean?

Q: What does 99.9% uptime actually mean?

99.9% uptime allows your website to be offline for up to 8 hours and 46 minutes a year, or around 43 minutes a month, while the host still keeps its promise. The figure sounds close to perfect, but every extra nine after the decimal point cuts the allowed downtime by ninety per cent.

Quick answer

99.9% uptime allows your website to be offline for up to 8 hours and 46 minutes a year, or around 43 minutes a month, while the host still keeps its promise. The figure sounds close to perfect, but every extra nine after the decimal point cuts the allowed downtime by ninety per cent.

The numbers behind the percentage

Uptime is the share of time your website is online and reachable. Hosting companies love a big round percentage, so it helps to turn it into time you can actually picture.

Allowed downtime

99% uptime3 days 15 hours a year (7.2 hours a month)

99.5% uptime1 day 20 hours a year (3.6 hours a month)

99.9% uptime8 hours 46 minutes a year (43 minutes a month)

99.95% uptime4 hours 23 minutes a year (22 minutes a month)

99.99% uptime53 minutes a year (4 minutes a month)

Monthly figures are based on a 30-day month. The gap between 99% and 99.9% looks tiny on paper, but in practice it is the difference between a few days offline and a single evening.

Read the small print

An uptime guarantee is a promise about compensation, not a promise that nothing will go wrong. A few things are worth checking:

What they pay back. Usually a credit off next month's hosting bill, not money for the enquiries or sales you lost.
Whether you have to claim. Many hosts only give a credit if you notice the outage and ask for it within a set time.
What does not count. Scheduled maintenance is often excluded, and so are problems caused by your own website or plugins.
What is being measured. "The server is up" and "your website loads properly" are not always the same thing.

So what should a small business look for?

For most local business websites, a reputable host offering 99.9% is perfectly sound. Beyond the percentage, what matters more is how quickly problems are spotted and fixed, whether maintenance happens at quiet times of night, and whether someone is monitoring your site so you are not the first to find out it is down.

A cheap host promising 99.99% with no monitoring and slow support is a worse deal than a good host promising 99.9% who answers the phone. We explain why prices vary so much in why is one hosting company cheaper than another?

The takeaway

99.9% uptime still allows nearly nine hours offline a year.
Guarantees usually pay out as hosting credit, and often only if you claim.
Monitoring and fast support matter more than an extra nine on the percentage.

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