Uptime is the share of a period during which a component worked for customers. Compute it per component, count partial outages by a rule you publish, and say how maintenance is treated. If you choose a definition that hides real customer pain, readers will notice the first time they are affected.
The basic formula
Uptime percent equals the minutes in the period without a qualifying outage, divided by total minutes in the period, times 100. In a 30 day month there are 43,200 minutes. Ten minutes of downtime is about 99.98 percent. Four hours is about 99.44 percent. The math is easy. The choices around it are what matter.
Decide what counts
Write down answers to these.
- Down versus degraded. Does a partial outage count in full, in part, or not at all? A common honest approach is to count a partial outage by the share of requests or customers affected, if you can measure it.
- Which signal? Measure from outside your network, at a customer facing endpoint, not from a health check on the server.
- Maintenance. If scheduled maintenance blocks customers, say clearly whether it is excluded. Excluding it is common, but state it.
- Upstream causes. If a provider failure breaks your service, it is still downtime for the customer.
- Granularity. Per component, not one blended number. A blended figure hides the weak part.
Present it carefully
Show the period, the components, the definition link and the incidents behind the numbers. Avoid rounding up. If the number is 99.94, do not display 99.9 percent as if it were a clean figure unless that is your stated target.
Do not confuse with a contractual commitment
A public number is a measurement. Any service level commitment in a contract has its own definition, credits and exclusions. Make sure the two do not contradict each other, and do not advertise a figure you are not willing to stand behind. Have legal read both.
Keep the data
Keep the raw monitoring results so you can show how each figure was reached when a customer asks.
Keep honest trend lines
If you change the measurement method, mark the change on the chart. Do not compare numbers before and after as if they mean the same thing.
Quick check
Is 99.9 percent a lot of downtime?
In a 30 day month it allows about 43 minutes. Whether that is acceptable depends on what your customers do with the service.
Should security incidents lower uptime?
If customers could not use the component, yes. Availability is availability, whatever the cause.
Last reviewed: 19 October 2026.
