SLA Uptime and Downtime Calculator

What this tool does

Each extra nine cuts the allowed downtime by ten: 99.9 % leaves almost nine hours a year, 99.99 % under an hour, and 99.999 % barely five minutes — less time than it takes most teams to notice an alert. The month here is an average month (a twelfth of a 365.25-day year); a contract may define it as the calendar month and exclude planned maintenance, so read the SLA's own definition. Availabilities of chained services multiply, which is why a system rarely beats its weakest dependency.

Formula

downtime = (1 − availability) × period · 1 year = 365.25 days, 1 month = 1/12 year

Variables

Worked example

Limitations

• The calculation runs at full precision and only the display is rounded. If you copy an intermediate value and retype it, small differences can appear.
• The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.