99.99% uptime four nines

Four nines allows four minutes and nineteen seconds of downtime a month. That is less time than most teams take to acknowledge a page, let alone fix anything.

4m 19s of downtime allowed per month

99.99% uptime by period

A month is taken as 30 days, a quarter as 90 days and a year as 365 days.

Period	Allowed downtime	Required uptime
Per day	9s	23h 59m
Per week	1m	6d 23h
Per month	4m 19s	29d 23h
Per quarter	12m 58s	89d 23h
Per year	52m 34s	364d 23h

Where 99.99% is used

Enterprise commitments, payment infrastructure, and the availability tier cloud providers publish for their own managed services. Rarely offered by small teams, and rarely achieved by teams that offer it.

What it demands

Redundancy at every layer with no manual step in the recovery path. At this tier a human cannot be in the loop: by the time a person reads the alert, the monthly budget is spent. Deploys have to be safe by construction, because a bad release is a breach.

One step either way

Dropping to 99.95% widens the monthly budget to 21m 36s. Moving up to 99.999% cuts it to 26s.

Measuring it

You cannot report on a service level you are not measuring at a finer resolution than the budget itself. At 99.99% the monthly allowance is 4m 19s, so a check interval anywhere near that figure will miss breaches entirely. Work out your own numbers, or monitor it continuously from four regions, free to start.

Other service levels

Compare the tiers

Every common service level, and the downtime each one allows per month.

90% 3d / month one nine 95% 1d 12h / month 99% 7h 12m / month two nines 99.5% 3h 36m / month 99.9% 43m 12s / month three nines 99.95% 21m 36s / month 99.999% 26s / month five nines

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