Uptime Calculator

Enter an uptime percentage (like 99.9%) to find the exact downtime it allows per year, month, week, and day.

Uptime Calculator

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Uptime target (%)

Downtime per year	8h 45m 58s
Downtime per month	43m 50s
Downtime per week	10m 4s
Downtime per day	1m 26s

The formula

Downtime = Total time period x ((100 - Uptime %) / 100)

Example

99.9% uptime ("three nines"): allowed downtime = 8.76 hours/year ≈ 8h 45m 58s per year, or about 43 minutes per month.

Step-by-step guide

Enter your target or actual uptime percentage.
Read the equivalent allowed downtime across different time periods.

Why each additional "nine" is a much bigger commitment than it looks

Moving from 99% to 99.9% looks like a tiny 0.9 percentage point improvement on paper, but it represents a 10x reduction in allowed downtime - from about 3.65 days a year down to under 9 hours. Each additional nine (99.99%, 99.999%) again cuts the allowed downtime by another factor of 10, which is exactly why "five nines" (99.999%) reliability, allowing only about 5 minutes of downtime per year, is considered an extremely demanding engineering target reserved for critical systems.

Common mistakes

Assuming a small percentage difference (like 99% vs 99.9%) means a similarly small difference in real downtime - each additional nine represents a full order-of-magnitude reduction, not an incremental one.

Confusing a monthly SLA calculation with an annual one - a service that meets 99.9% every individual month isn't automatically the same as 99.9% measured across a full year, since months have different lengths.

Frequently asked questions

What uptime percentage is considered "good"?

It depends entirely on the system - many commercial cloud services target 99.9% to 99.99% ("three to four nines"), while systems where downtime is life-critical (like some telecom or medical infrastructure) may target 99.999% or higher.

Does this account for planned maintenance windows?

No - this calculates total allowed downtime regardless of cause. Many real-world SLAs (Service Level Agreements) specifically exclude scheduled maintenance from the downtime count, which is worth checking in your specific contract.

How is uptime percentage actually measured in practice?

Typically as the percentage of time a system was available and functioning correctly out of the total time in the measurement period, often tracked through automated monitoring tools that log outages.

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