Glossary · Reliability metrics
Uptime is the time a website, API or other service is available and working as expected. It is usually given as a percentage of a period, such as 99.9% of a month.
Uptime is measured from the outside: a monitor sends a request on a schedule and records whether the answer was right. The percentage is the working time divided by the measured time, so the result depends on how often you check and on what counts as working: any answer, a specific status code, or a page that contains the right text.
A server can be running while the service is down for its users. A broken database connection, an expired certificate or a DNS mistake leaves the machine up and the website unusable. That is why uptime monitoring checks what users reach, not the host’s own uptime counter, which only says how long it has run since the last restart.
Dashboards and agreements usually report uptime per calendar month, which is also the period an SLA’s service credits are calculated over. The nines show how little downtime the higher targets allow.
Uptime % = (measured time − downtime) ÷ measured time × 100
Example: An average month has 2,629,800 seconds (365.25 days ÷ 12). 43 minutes and 49 seconds of downtime in it leaves 99.9% uptime.
Uptimecheck checks websites, APIs, ports and ping targets as often as every minute from Stockholm, and confirms every failure with a second check before it counts. Uptime is the monitored time without a confirmed outage: maintenance windows don’t count against it, and time a monitor was paused is left out instead of counted as up or down.
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Guides 5 min read
Uptime monitoring checks your website or API on a schedule and alerts you when it fails. How checks work, which interval to choose and what uptime percentages mean in minutes.
ReadGuides 5 min read
The uptime formula, worked examples with incidents and maintenance, how to combine the uptime of several components, and how uptime, availability and reliability differ.
ReadMonitoring 2 min read
Downtime costs revenue and customer trust. Why every business website needs uptime monitoring, and how to set it up so problems are found in minutes.
ReadFor most websites and SaaS products, 99.9% (about 44 minutes of downtime a month) is a common target, and 99.95% or 99.99% for services others depend on. Each extra nine allows ten times less downtime and costs more to reach, so pick the level your users need.
No. Server uptime is how long the machine has run since its last restart. Website uptime is whether visitors could use the site. A server with months of uptime can still serve errors.
Only if your definition says so; many SLAs leave announced maintenance out. In Uptimecheck, monitors in a maintenance window aren’t checked, so that time never counts as downtime.
Set up your first monitor in under a minute, or look around the live demo first.
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