What an uptime SLA is really worth β downtime hours and revenue lost.
βThree ninesβ sounds abstract until you convert it to hours of outage and dollars lost. This tool does exactly that, and shows what buying the next nine saves. Model the redundancy spend on the container hosting calculator.
The API Downtime Cost Calculator converts an uptime SLA percentage into the amount of outage you should expect over a year and the revenue that downtime puts at risk. Enter your target uptime β say 99.9% β and the calculator derives the allowed downtime, roughly 8.76 hours per year, since every additional nine cuts that figure by about a factor of ten. It then combines your annual revenue at risk with the share of revenue lost during an outage to estimate the dollar cost of that downtime, showing what each incremental nine of reliability is actually worth to you.
The main trade-off is that higher uptime targets cost progressively more to reach, so compare the modeled savings against that expense before committing. Moving from 99% to 99.9% may save meaningful revenue, but the jump to 99.99% often costs far more than the few extra hours of protection returns. Set the revenue lost during outage input honestly: not all traffic converts to sales, and some demand simply shifts to a later time rather than disappearing, so a realistic percentage keeps the estimate useful.
99% uptime allows 3.65 days of downtime a year; 99.9% allows 8.8 hours; 99.99% allows 52.6 minutes; 99.999% (five nines) allows just 5.3 minutes. Each additional nine cuts allowed outage roughly tenfold β and usually multiplies the engineering cost to achieve it.
Only if the revenue or reputation saved exceeds the cost of the redundancy needed to hit it. This calculator shows the annual money at stake per nine so you can compare it against multi-region failover, hot standbys and on-call cost. For many internal tools 99.9% is plenty; for checkout flows every minute counts.