SLA Uptime Calculator
That extra "9" costs a fortune. See exactly how much downtime each SLA level allows.
%
Allowed Downtime
Per year8h 45m 36s
Per month43m 48s
Per week10m 4.8s
Per day1m 26.4s
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The "Nines" Table — IT's Most Important Reference
| SLA | Nines | Downtime/Year | Downtime/Month |
|---|---|---|---|
| 99% | Two 9s | 3.65 days | 7.3 hours |
| 99.5% | — | 1.83 days | 3.65 hours |
| 99.9% | Three 9s | 8.7 hours | 43.8 min |
| 99.95% | — | 4.38 hours | 21.9 min |
| 99.99% | Four 9s | 52.6 min | 4.4 min |
| 99.999% | Five 9s | 5.26 min | 26.3 sec |
Each additional "9" roughly divides downtime by 10 but can increase infrastructure costs by 10× or more. The jump from 99.9% to 99.99% is one of the most expensive upgrades in cloud computing.
The Cost of Downtime
Amazon's estimated cost of downtime: ~$13.22 million per hour. For a mid-size e-commerce site doing $10M/year, one hour of downtime costs ~$1,142. This is why SLA negotiations are worth millions.
How This Relates to "10% Off"
A 90% SLA (only "one 9") means your service can be down 36.5 days per year — that's 10% downtime. If someone offered you a service that's "down 10% of the time," you'd probably say no. But 90% uptime sounds high until you do the math.
Frequently Asked Questions
99% = "two nines", 99.9% = "three nines", etc. Each additional 9 means 10× less downtime. Most production systems target at least three nines (99.9%).
It depends on the provider. Some SLAs exclude scheduled maintenance windows. Always read the fine print to know if maintenance counts toward your uptime guarantee.
Most cloud providers offer service credits — typically 10-30% of your monthly bill for the affected service. Rarely does it cover actual business losses from downtime.
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