Uptime SLA Calculator

Convert an availability percentage into allowed downtime per day, month and year.

Please note: An estimate based on the figures you entered. Real-world results vary with conditions this calculation cannot see, so treat it as a starting point rather than a final answer.

What the Uptime SLA Calculator does

An availability percentage translates directly into an allowance of downtime. The jump between tiers is steeper than it looks: going from 99.9% to 99.99% cuts the yearly budget from nearly nine hours to under an hour, and each further nine is another factor of ten.

Formula

Downtime = (1 − Availability) × Period length
Nines = −log₁₀(1 − Availability)
Series availability = A₁ × A₂ × … × Aₙ

Inputs explained

Input	Unit	Required	Notes
Start from	one of 2 options	Yes	—
Availability	%	In some modes	Accepts 0 or more, up to 100. Shown Start from is An availability target.
Downtime	minutes	In some modes	Accepts 0 or more. Shown Start from is An amount of downtime.
Downtime measured over	one of 4 options	In some modes	Shown Start from is An amount of downtime.
Components in series	number	Optional	Availability multiplies across dependencies, so more components means less overall uptime. Accepts 1 or more.

How to use it

Choose Start from.
Fill in the remaining inputs the form shows for your choice.
Optionally add Components in series.
Select Calculate.

Worked example

A 99.9% availability target — three nines.

Availability: 99.9%

0.1% of a year is 8 h 45 min 36 s. That is 43 min 12 s a month, 10 min 5 s a week, or 1 min 26 s a day.

Frequently asked questions

What does "five nines" actually mean?

99.999% availability — about 5 minutes 15 seconds of downtime a year. It demands full redundancy, automated failover and no single point of failure.

Why does adding components reduce availability?

Because in a series chain any one failure takes the whole service down, so the availabilities multiply. Five 99.9% components give 99.5%, not 99.9%.