Guides 4 min read
The Cost of Website Downtime: How to Calculate Yours
What does an hour offline really cost? A simple formula for the direct and hidden costs of downtime, worked examples and what uptime percentages mean in money.
ReadGlossary · Reliability metrics
What is downtime?
Downtime is the time a service is unavailable or not working correctly for its users, whether it is fully offline, returning errors or too broken to use.
How it works and why it matters
Unplanned downtime comes from outages: crashed servers, failed deploys, expired certificates or domains, DNS mistakes, overloaded databases or a provider’s outage. Planned downtime is maintenance you schedule and, ideally, announce in a maintenance window.
Decide what counts as down before it happens. A 503, a timeout and a page that loads but shows an error message are all downtime for a visitor. A monitor only sees what it is told to check, so check the status code and, for important pages, a keyword that only appears when the page works.
The cost of downtime grows with its length and with how many people notice before you do: lost sales, support tickets, SLA credits and lost trust.
Formula
Allowed downtime = period × (100% − uptime target)
Example: At 99.5% uptime, an average month (30.44 days) allows 3 hours, 39 minutes and 9 seconds of downtime; at 99.9% it allows 43 minutes and 49 seconds.
How Uptimecheck helps
Uptimecheck counts downtime from a confirmed outage to the first successful check after it; a single failed check that a second check doesn’t confirm never counts. Recovery alerts say how long the monitor was down, and reports show downtime per monitor next to its uptime.
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Read more in the guides
Guides 5 min read
What Is Uptime Monitoring? How It Works and What 99.9% Really Means
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 8 min read
503 Service Unavailable: What It Means and How to Fix It
A 503 Service Unavailable error means the server is reachable but cannot handle the request right now. The common causes, how to fix each one and how monitoring catches 503s early.
ReadQuestions
What is the difference between downtime and an outage?
They are often used as the same thing. An outage is the event, the service failing; downtime is the time it lasts. One outage of 20 minutes is 20 minutes of downtime.
Is a slow website down?
Usually not in an SLA, unless it sets a response time limit. For users a page that takes 30 seconds is as good as down, so track slow responses separately. In Uptimecheck, slow time doesn’t count as downtime; it has its own slow alerts.
How do I calculate the cost of downtime?
Add lost revenue (revenue per hour × hours down), the cost of the people fixing it, SLA credits and the work afterwards. The free downtime cost calculator does it from your own numbers.
More from Reliability metrics
All terms-
The nines (99.9% uptime)
Nines of availability Availability targets counted in nines, from 99% to 99.999%, and the downtime each allows. Read the definition : The nines (99.9% uptime) -
SLA
Service level agreement A contract that promises a service level, such as 99.9% uptime, and credits when it is missed. Read the definition : SLA -
SLO
Service level objective An internal reliability target, with the error budget it leaves. Read the definition : SLO
Downtime is obsolete.
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