Reliability · Uptime
Uptime SLA downtime calculator.
Pick an availability target and see how many minutes or seconds of downtime it allows per day, week, month, quarter and year.
Inputs
Result
Enter the values above.
What does 99.9% uptime mean?
Availability is the share of a period a service is up. Allowed downtime is the period length times one minus the target: for 99.9% over a 30-day month that is 43,200 minutes x 0.001 = 43.2 minutes. Google's SRE Book availability table gives the same 43.2 minutes per month, 8.76 hours per year and 1.44 minutes per day for 99.9%, and 52.6 minutes per year for 99.99%. Those figures assume no planned downtime. This tool uses a 30-day month and a 365-day year, so a calendar month of 31 days or a contract that counts differently will give a slightly different allowance. Check how your SLA defines its measurement window.
Worked example. 99.95% leaves 0.05% of a 30-day month: 43,200 x 0.0005 = 21.6 minutes.
Frequently asked questions
How much downtime is 99.9% uptime per month?
43.2 minutes in a 30-day month, 8.76 hours per year and 1.44 minutes per day, matching the Google SRE availability table.
How much downtime is five nines (99.999%)?
About 25.9 seconds per 30-day month and 5.26 minutes per year (Google SRE availability table).
Does scheduled maintenance count?
The source tables assume no planned downtime. Many commercial SLAs exclude maintenance windows, so read your own contract.
Why do other calculators show 43 minutes 50 seconds?
They use a 30.44-day average month instead of 30 days. Neither is wrong; use the one your SLA names.
Sources
Checked
- Google SRE Book: Appendix A, Availability Table
- AWS Well-Architected Reliability Pillar: Availability
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.