SLA Uptime Downtime Calculator
Convert an SLA uptime percentage into allowed downtime per day, week, month, quarter and year — and back.
About this tool
SLA Uptime Downtime Calculator
Convert an SLA uptime percentage into allowed downtime per day, week, month, quarter and year — and back.
The SLA Uptime Downtime Calculator converts an SLA availability percentage into the exact downtime it permits — allowed downtime = (1 − uptime% ÷ 100) × period length — reported per day, week, month, quarter and year. It is built for SREs, platform engineers and anyone negotiating or monitoring a service-level agreement, and it also works in reverse: enter real downtime to get the uptime percentage achieved. Periods use the Gregorian mean year of 365.2425 days so all five figures stay consistent.
How to use SLA Uptime Downtime Calculator
- 1
Open SLA Uptime Downtime Calculator on AltFTool — it loads instantly in your browser.
- 2
Enter your availability in 'Uptime target (%)' or tap a nines preset chip — 99%, 99.5%, 99.9%, 99.95%, 99.99% or 99.999%.
- 3
There is no calculate button — the budget recomputes as you type; for the reverse check fill 'Actual downtime (minutes)' and 'Over which period'.
- 4
'Allowed downtime per month' headlines the result with per-day, week, quarter and year rows below; press 'Copy result' to copy all five figures.
Why use SLA Uptime Downtime Calculator
All five windows at once
Daily, weekly, monthly, quarterly and yearly budgets from one percentage, mutually consistent.
Works in reverse
Enter actual downtime minutes over any window and get the achieved uptime percentage.
Standard nines presets
One tap for 99%, 99.5%, 99.9%, 99.95%, 99.99% and 99.999% targets.
Common use cases
- An SRE translating a proposed 99.95% SLO into a monthly error budget before agreeing to it in a service review
- A SaaS buyer comparing vendor SLAs by seeing that 99.5% allows about 3.7 hours of downtime a month while 99.9% allows about 44 minutes
- An on-call engineer entering last month's 38 minutes of outage to check whether the 99.9% target was met
Frequently asked questions
How much downtime does 99.9% uptime allow?
About 43 minutes 50 seconds per month and 8 hours 46 minutes per year. The formula is (1 − 0.999) × period length, using an average month of 30.44 days; per day it is roughly 1 minute 26 seconds.
What is the difference between 99.9% and 99.99% uptime?
Roughly a factor of ten in allowed downtime: 99.9% permits about 8.8 hours of outage per year while 99.99% permits about 52.6 minutes. Per month that is about 43.8 minutes versus 4.4 minutes, which is why each extra nine gets significantly more expensive to engineer.
How do I calculate uptime percentage from downtime?
Divide downtime by the total length of the period, subtract from 1 and multiply by 100: uptime% = 100 × (1 − downtime ÷ period). For example, 30 minutes of downtime in a 30.44-day month is 100 × (1 − 30 ÷ 43,829) ≈ 99.932%.
Does a monthly SLA use 30 days or the calendar month?
It depends on the contract — many providers measure per calendar month, so February has a smaller minute count than January. This tool uses the Gregorian average of 30.436875 days per month so the daily, monthly and yearly figures agree; check your SLA's own definition of the measurement window and any maintenance exclusions before relying on a figure.
Embed this tool on your site
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