How is uptime percentage calculated?

Uptime percentage is calculated using the formula: Availability (%) = (Total Time - Downtime) / Total Time × 100. For example, if a service ran for 720 hours in a month with 43 minutes of downtime, the availability would be 99.9%.

How much downtime does a 99.9% SLA allow?

A 99.9% SLA (three nines) allows approximately: 43.8 minutes per month, 10.1 minutes per week, 1.44 minutes per day, or 8.76 hours per year. This is the standard for most production services.

What is the difference between 99.9% and 99.99% availability?

99.9% (three nines) allows ~43.8 minutes of downtime per month, suitable for standard production applications. 99.99% (four nines) allows only ~4.38 minutes per month, requiring redundant infrastructure and high availability. The difference can cost significantly more in infrastructure.

What is an SLA and how does it relate to downtime?

An SLA (Service Level Agreement) is a contract that defines the expected service level, including the guaranteed uptime percentage. For example, a 99.9% SLA means the provider guarantees the service will be available 99.9% of the time, and any downtime below that threshold may result in credits or penalties.

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Downtime Calculator

Common SLA levels and their meaning

SLA Level	Downtime/day	Downtime/month	Downtime/year	Service type
99%	14.4 min	7.2 horas	3.65 días	Internal tools
99.9%	1.44 min	43.8 min	8.76 horas	Production standard
99.99%	8.64 seg	4.38 min	52.6 min	Critical services
99.999%	864 ms	25.9 seg	5.26 min	Telecom, banking

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Downtime Calculator

Common SLA levels and their meaning

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