Five Nines SLA
99.999% Uptime Calculator

"Five nines" refers to 99.999% availability - the percentage contains five 9 digits. It is the highest SLA tier commonly advertised by major cloud and telecom providers.

99.999% SLA allows about 5 minutes and 15 seconds of downtime per year (using a 365-day year), or roughly 864 milliseconds per day.

Five nines (99.999%) is historically the reliability target for the public switched telephone network, since a dial tone is expected to be available almost without exception. Emergency services, financial exchanges, and other life- or money-critical systems adopted the same benchmark.

Rarely, and usually not cost-effective. A single deployment mistake or DNS propagation delay can consume the entire annual budget in one incident. Five nines is generally reserved for infrastructure providers, telecom carriers, and systems where downtime has severe financial or safety consequences.

Five nines allows roughly 10 times less downtime than four nines: about 5 minutes 15 seconds per year versus about 52 minutes 34 seconds. Going from four to five nines usually requires active-active multi-region architecture rather than simple multi-zone redundancy.