Glossary · Monitoring

Downtime

Downtime is the period during which a website, application or service is unavailable or not working properly for its users.

Updated October 6, 2026

Downtime is the time a system cannot perform its intended function for users. It can be unplanned, caused by failures, bugs, attacks or expired certificates, or planned, such as scheduled maintenance. Uptime is its opposite.

Why it matters

Downtime costs revenue, trust and search visibility. Even short outages interrupt customers, and long ones can hurt rankings if crawlers repeatedly see errors. Teams measure it to set targets and compare against SLAs. Definitions vary: some counts only full outages, while others include severe slowness. Always check how a contract or report defines it.

Example

Converting an availability target into allowed downtime for a 30-day month (43,200 minutes):

99%     -> 432 minutes
99.9%   -> 43.2 minutes
99.99%  -> 4.32 minutes

If monitoring records failures from 09:12 to 09:38, that is 26 minutes of downtime.

Common mistakes

  • Counting only complete outages and ignoring partial failures.
  • Forgetting that planned maintenance may or may not count under an SLA.
  • Measuring from one location only.
  • Estimating downtime from memory instead of monitoring timestamps.

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Keep reading

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