Five Nines Availability Table — Uptime & Downtime Reference

Availability	Nines	Per year	Per month	Per week	Per day
90%	One nine	36d 12h	73h	16h 48m	2h 24m
95%	—	18d 6h	36h 30m	8h 24m	1h 12m
99%	Two nines	3d 15h 36m	7h 18m	1h 40m	14m 24s
99.5%	—	1d 19h 48m	3h 39m	50m 24s	7m 12s
99.9%	Three nines	8h 45m 36s	43m 49s	10m 4s	1m 26s
99.95%	—	4h 22m 48s	21m 54s	5m 2s	43s
99.99%	Four nines	52m 35s	4m 22s	1m 0s	8.6s
99.995%	—	26m 17s	2m 11s	30.2s	4.3s
99.999%	Five nines	5m 15s	26.3s	6.0s	0.86s
99.9999%	Six nines	31.5s	2.6s	0.6s	0.086s

How to read this table

Each row shows the maximum cumulative downtime allowed at that availability tier before an SLA breach. For example, a 99.9% SLA allows 8 hours 45 minutes of downtime per year — roughly one major incident before hitting the annual limit.

Note that these are cumulative limits. Multiple short incidents count toward the total just as much as a single long outage.

What availability tier should you target?

Most consumer web applications target 99.9% (three nines). Mission-critical financial or healthcare systems often target 99.99% (four nines). Achieving five nines (99.999%) requires redundant systems, automated failover, and extremely disciplined change management — less than 6 minutes of downtime per year leaves very little room for unplanned maintenance.

Use the Availability Calculator to compute exact downtime for any uptime percentage.