99.9% uptime three nines

Where 99.9% is used

The default published SLA across most B2B SaaS, and the level most managed database and hosting providers commit to on their standard tiers. If you are writing your first SLA, this is almost certainly the number you want.

What it demands

Sub-minute detection and a practised response. Forty-four minutes a month is one meaningful incident. If your monitoring checks every five minutes, detection alone can eat an eighth of the annual budget before anyone opens a laptop.

One step either way

Dropping to 99.5% widens the monthly budget to 3h 36m. Moving up to 99.95% cuts it to 21m 36s.

Measuring it

You cannot report on a service level you are not measuring at a finer resolution than the budget itself. At 99.9% the monthly allowance is 43m 12s, 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.