Q: My monitor reports 99.9% uptime. That's excellent, right?

Q: My monitor reports 99.9% uptime. That's excellent, right?

A: It sounds great until you do the math. 99.9% allows 43.8 minutes of downtime per month, or about 8.76 hours per year. For a checkout page or API, 44 minutes in one bad afternoon is a real incident, not a rounding error.

The myth is treating any number with lots of nines as automatically good. Context decides. 99.9% is fine for a blog; 99.99% (about 4.4 min/month) is the floor for paid services; 99.999% means under 26 seconds a month and usually needs serious redundancy.

Recommendation: pick your target from business impact, then size your interval and alerting to actually catch breaches of it.

Anticipating the follow-up: yes, your monitor's own gaps count against measurement accuracy.

Got a question? Drop it in the comments.