Uptime reference

99.999% uptime five nines

Five nines is 26 seconds a month. It is quoted far more often than it is delivered, and it is usually quoted by people who have not worked out what it costs.

26s of downtime allowed per month

99.999% 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	1s	23h 59m
Per week	6s	6d 23h
Per month	26s	29d 23h
Per quarter	1m 18s	89d 23h
Per year	5m 15s	364d 23h

Where 99.999% is used

Telecoms, core payment rails, and safety-critical systems. When a SaaS vendor claims five nines, check whether the SLA measures the whole service or a narrow control-plane endpoint, and check what the remedy is.

What it demands

Active-active across regions, automated failover measured in seconds, and an organisation that treats a single bad deploy as an incident. The cost is not the infrastructure, it is the engineering discipline it forces on everything else.

One step either way

Dropping to 99.99% widens the monthly budget to 4m 19s.

Measuring it

You cannot report on a service level you are not measuring at a finer resolution than the budget itself. At 99.999% the monthly allowance is 26s, 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 99.99% 4m 19s / month four nines

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