SLA math
99.9% uptime: how much downtime is that?
Three nines is the most common public SaaS target. It still allows nearly a full work day of downtime each year — planned or not.
Target
99.9%
Allowed downtime / year
8.8 hours / year
Per month (avg)
43.8 minutes
Who uses it
Who usually picks 99.9%
Typical for early B2B SaaS and marketing sites where a few hours a year is painful but survivable.
Caveats
Read this before you print it on a sales slide
- SLAs often exclude planned maintenance — read the fine print
- Customer-experienced downtime can exceed probe downtime (partial outages)
- A monthly error budget is easier to manage than an annual lump
FAQ
99.9% uptime, answered
Exact minutes for three nines, whether it is enough for SaaS, and how monitoring helps defend it.
Keep reading
Related SLA and cost tools
- What counts as good uptime
99.9% vs 99.99% vs 99.999% in plain English.
- How to write an uptime SLA
Promises you can actually keep.
- Downtime cost calculator
Turn outage minutes into dollars.
- 99.95% uptime
4.4 hours / year
- 99.99% uptime
53 minutes / year
- 99.999% uptime
5 minutes / year
Defend 99.9% with clearer pages
False pages waste the people who keep a 99.9% promise. Tallwatch opens incidents when at least two regions agree — Free includes consensus.