Reliability · Uptime
Uptime percentage calculator.
Enter the downtime you had in a period and get the availability achieved, plus whether it meets your SLA.
Inputs
Result
Enter the values above.
How to calculate uptime percentage
Availability is available time divided by total time (AWS Well-Architected Reliability Pillar). Uptime % = (1 - downtime / period) x 100. With 30 minutes of downtime in a 30-day month (43,200 minutes) the result is (1 - 30 / 43,200) x 100 = 99.9306%, which meets a 99.9% SLA that allows 43.2 minutes.
This is time-based availability. If your service is only partly down, or load varies, Google's SRE Book suggests a request-based measure (successful requests divided by valid requests) instead; use the error budget calculator for that.
Frequently asked questions
How do I calculate uptime from downtime?
Divide downtime by the period length, subtract from 1 and multiply by 100. 30 minutes down in a 30-day month is 99.9306%.
What counts as downtime?
Whatever your SLA defines. The AWS guidance applies the strictest reading, counting any time the application is not operating normally; many contracts exclude maintenance.
What if only some users were affected?
A partial outage is better measured by failed requests over total requests than by minutes. See the error budget calculator.
What are nines?
Shorthand for the count of leading 9s: 99.9% is three nines and 99.999% is five (AWS Well-Architected).
Sources
Checked
- AWS Well-Architected Reliability Pillar: Availability
- Google SRE Book: Appendix A, Availability Table
- Google SRE Book: Embracing Risk
Formulas follow the sources above. Periods use a 30-day month and a 365-day year. Runs entirely in your browser; nothing you type is sent or stored.
Scope
Planning estimates only. Your SLA contract defines its own measurement window, exclusions and remedies, and those override these generic figures. Theoretical availability assumes independent failures.