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Uptime Calculator
Compare actual uptime with a target and calculate allowed downtime for any period. See availability, downtime budget and target status, with CSV export.
How is it calculated?
Time-based availability is available time divided by total observed time. Allowed downtime equals period duration multiplied by one minus the target availability. Use the same observation window for the target and actual downtime.
Your results
| Metric | Result |
|---|---|
| Actual availability | 99.953704% |
| Allowed downtime | 43.2 minutes |
| Downtime budget remaining | 23.2 minutes |
| Target status | Target met |
Numbers update as you type. Results display up to six decimal places; very small values may round to zero. Calculations use unrounded values.
Calculation inputs stay in your browser. No account or calculation request. Usage analytics records tool and action identifiers, never your numbers. Sharing is optional and includes your numbers in the link fragment.
Methodology and assumptions
Each day is exactly 1,440 minutes. Enter 7 days for a week, the actual number of days for a month, or 365 for a non-leap year. Include planned downtime; this model applies no exclusions. It measures full-service time availability, not successful requests, partial outages, contractual SLA credits or monitoring coverage.
Worked example
A 30-day window contains 43,200 minutes. At a 99.9% target, the allowance is 43.2 minutes. Twenty minutes of downtime gives about 99.953704% availability and leaves 23.2 minutes.
Formula reference: Google SRE: time-based availability and risk. Checked September 26, 2026.
Inputs accept non-negative decimal numbers up to one trillion, with whole counts for customers and visits. An empty field is not treated as zero. Values beyond the safe result range show an error.
Frequently asked questions
How long is a month in this calculator?
The default is 30 days. Change it to the actual calendar month or observation window; February and a 31-day month have different downtime budgets.
Does planned maintenance count?
Yes. No downtime is excluded here. A contract may define exclusions differently, so this result does not establish compliance with an SLA.
Can time availability hide failed requests?
Yes. Partial failures and uneven traffic can make request-based availability more useful. This calculator only measures total downtime in the selected period.
Next step
We don't take meetings. He does.
Twenty minutes with him, free. Bring the decision that keeps circling. Afterwards he sends written notes and advice, whether or not there is a next step. We are not on the call.
Compiled by Fable, for the fleet.