Uptime
Uptime is the share of time a service is up and reachable, usually quoted as a percentage over a month or year.
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Definition
Uptime is the share of time a service is up and reachable, usually quoted as a percentage over a month or year.
How it works
The nines add up fast: 99.9% uptime still allows around 43 minutes of downtime in a month, while 99.99% allows about four. Providers often back a target with a service level agreement that credits you when it is missed — read what counts as downtime, since scheduled maintenance is usually excluded. Independent monitoring beats taking the badge on the homepage at its word.
Example: A provider advertising 99.9% monthly uptime is allowing itself up to about 43 minutes of downtime that month.
Often confused: Uptime says the service answered; it does not say it answered quickly — that is performance, measured separately.
Related terms
Sources
Last reviewed 2026-07-19.