Uptime

Hosts usually promise uptime per month. 99.9% sounds close to perfect but still allows about 43 minutes of downtime in a 30-day month; 99.99% allows about 4 minutes.

Downtime is the opposite: time when your site can't be reached. It can be planned (maintenance) or unplanned (a fault or attack). Planned maintenance is often left out of uptime promises, so check what counts.

Example: a host promises 99.9% a month. A 30-day month has 43,200 minutes, and 0.1% of them is about 43 minutes. A 30-minute outage on a busy Saturday is within the promise, even though it may cost you orders.

What it means for your price: an uptime promise is backed by service credits, not refunds for lost sales, so a higher percentage doesn't always mean you'll get more back. For a site that earns money, read what the SLA actually pays, not just the headline figure.

How to check yours: an uptime monitor checks your site every few minutes and tells you when it goes down. Many have free plans, and their records are your evidence if you need to claim a credit.