SaaS / Reliability
Uptime and SLA Calculator: Downtime for 99.9%, 99.99%, and More
Turn an availability target such as 99.9% into the downtime it allows each day, week, month, and year, or turn a period of downtime into the availability it leaves, with a table of the common nines.
Uptime and SLA Calculator: Downtime for 99.9%, 99.99%, and More: Allowed downtime is (1 − availability) × the period: at 99.9%, 0.1% of a 30.44-day month is 43.8 minutes, and of a year 8.77 hours. Each extra nine divides that by ten. In reverse, 43.8 minutes down in a month leaves 99.9% availability. Runs 100% locally in your browser with zero server file uploads.
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| Availability | A day | A month | A year |
|---|---|---|---|
| 99% | 14 min 24 s | 7 h 18 min | 3 days 16 h |
| 99.5% | 7 min 12 s | 3 h 39 min | 1 days 20 h |
| 99.9% | 1 min 26 s | 43 min 50 s | 8 h 46 min |
| 99.95% | 43.2 s | 21 min 55 s | 4 h 23 min |
| 99.99% | 8.6 s | 4 min 23 s | 52 min 36 s |
| 99.999% | 0.9 s | 26.3 s | 5 min 16 s |
Each extra nine cuts allowed downtime tenfold: 99.9% (three nines) allows 43.8 minutes a month and 8.77 hours a year, and 99.99% only 4.4 minutes a month. Months here average 30.44 days. Services that depend on each other multiply their availabilities: two 99.9% services in a chain give 99.8%. Check how your provider's SLA counts downtime: many exclude planned maintenance and short blips.
The nines
99% allows 7.3 hours a month, 99.5% 3.65 hours, 99.9% 43.8 minutes, 99.95% 21.9 minutes, 99.99% 4.4 minutes, and 99.999% 26 seconds.
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How to use it
- Choose availability to downtime, or downtime to availability.
- Enter the percentage or the minutes of downtime.
- Read the allowance or the availability, and compare with the table.
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Frequently asked questions
What do the nines mean?
The number of nines in the percentage: three nines is 99.9%, four nines 99.99%, five nines 99.999%, or about 5 minutes a year.
How do dependencies affect uptime?
Services in a chain multiply: two 99.9% services that both must work give 99.8%. Redundant copies do better: two 99% servers where one is enough give 99.99%.
Does the SLA count maintenance?
Often not: many SLAs exclude scheduled maintenance and outages shorter than a few minutes, so read how downtime is measured.
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