Unkillable Window

RELIABILITY, WITH THE MATH SHOWN

Put an outage in context.

Availability arithmetic and practical incident-record guides for small web teams. Clear measurement windows, explicit exclusions and reproducible calculations.

Website availability and downtime calculator →
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Make the next decision clearer.

01 / FIELD GUIDE

Define an availability measurement window

Percentages are meaningful only with a method.

Read the guide →02 / FIELD GUIDE

A small incident record that helps the next responder

Capture decisions and evidence without filling a giant form.

Read the guide →

Begin with your own evidence

Calculate observed availability from a defined measurement window and recorded downtime. Compare it with a target without treating a target as a guarantee.

Availability = (window minutes − downtime minutes) ÷ window minutes × 100. Allowed downtime at a target = window minutes × (1 − target ÷ 100). A 30-day window contains 43,200 minutes; 30 minutes downtime means 99.93056% observed availability.

The tool assumes the downtime total is correct and non-overlapping. Probe failures, partial outages, planned maintenance and contractual exclusions need a defined measurement policy. A result does not establish an SLA credit or prove a service was available to every visitor.

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