Uptime and SLA calculator
Enter an availability target to see how much downtime it allows each day, week, month, quarter and year, or switch modes and enter the downtime you had to get the availability you delivered.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Enter the availability target, such as 99.9.
- Read the allowed downtime for each period.
- To check a past period, switch the mode, enter the downtime and choose the period.
Allowed downtime = (100 − availability) ÷ 100 × period length
Availability = (1 − downtime ÷ period length) × 100
Periods: day 86,400 s, week 604,800 s, year 365.25 days, month = year ÷ 12, quarter = year ÷ 4. Times are rounded to the second once they pass a minute.
Worked example
At 99.9 % the unavailable share is 0.1 %, so a day allows 0.001 × 86,400 = 86.4 s (1 min 26 s), a month 0.001 × 2,629,800 = 2,629.8 s (43 min 50 s) and a year 0.001 × 31,557,600 = 31,557.6 s (8 h 45 min 58 s).
Tips
- An availability chain multiplies: two services at 99.9 % that both must work give about 99.8 % together.
- Monthly budgets are easier to act on than yearly ones; a single long outage can spend the whole month.
Frequently asked questions
How much downtime does 99.9 % allow?
About 1 minute 26 seconds a day, 43 minutes 50 seconds a month and 8 hours 46 minutes a year. Each extra nine divides the allowance by ten: 99.99 % allows about 4 minutes 23 seconds a month.
How long are a month and a year here?
A year is 365.25 days, which averages in leap years; a month is a twelfth of that (30.44 days) and a quarter a quarter of it. Contracts that count calendar months will differ by a few seconds or minutes.
How do I calculate the availability I delivered?
Switch to "Availability from downtime", enter the minutes of outage and the period. The formula is (1 − downtime ÷ period) × 100. For example, 30 minutes in a month gives 99.932 %.
What counts as downtime in an SLA?
That depends on the contract. Many exclude planned maintenance, count only outages longer than a few minutes, or measure from the customer's side. Read the definitions before comparing numbers.