How much downtime does 99.9% uptime allow?

99.9% uptime (three nines) allows approximately 8 hours 46 minutes of downtime per year, 43 minutes 50 seconds per month, and 10 minutes 5 seconds per week.

How much downtime does 99.99% uptime allow?

99.99% uptime (four nines) allows approximately 52 minutes 36 seconds of downtime per year, 4 minutes 22 seconds per month, and 1 minute 1 second per week.

What is five nines uptime?

Five nines (99.999% uptime) allows only 5 minutes 15 seconds of downtime per year. This is considered telco-grade reliability and requires active redundancy across multiple regions.

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Three nines

Period	Allowed downtime
Per day	1m 26s
Per week	10m 5s
Per month	43m 50s
Per year	8h 46m

What this means

99.9% ("three nines") is the most common SLA for indie SaaS — about 8h 46m of downtime per year is acceptable.
99.99% ("four nines") is what most enterprise buyers expect — under 53 minutes per year.
99.999% ("five nines") is telco-grade — less than 5m 15s of downtime per year. Practically impossible without active redundancy.
These numbers assume downtime is distributed evenly. A single deployment accident can consume your entire annual budget in one go.

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How SLA downtime is calculated

Allowed downtime = (1 − uptime%) × period in minutes. Monthly figures use a 30.44-day average; yearly figures use 365.25 days to account for leap years.

These numbers represent the budgetdefined in a service level agreement — the maximum downtime a provider is contractually permitted before penalties apply. They don't mean downtime is planned or expected; they define the worst-case limit.

Most monitoring tools (including SitePulse) report uptime as a rolling 30-day percentage based on successful checks, giving you a live view of where you stand against your SLA target.