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Uptime SLA Calculator

Find allowed downtime for an SLA.

How it is calculated

The unavailable share is down = 1 − SLA ÷ 100. Allowed downtime per year is down × 365.25 × 24 × 60 minutes; the 365.25 averages in leap years. Per month it is that figure divided by 12, and per day it is down × 24 × 60 minutes. The SLA must be a percentage between 0 and 100, entered as 99.95, not 0.9995. All results are in minutes, rounded to two decimals; divide by 60 for hours. The tool gives the maximum outage a percentage permits. It does not know how your contract measures uptime, which maintenance windows are excluded, or what credits you get when the target is missed.

Worked example

An SLA promises 99.95% uptime. The downtime share is 1 − 0.9995 = 0.0005. Per year: 0.0005 × 525,960 minutes (365.25 × 24 × 60) = 262.98 min, which is about 4 hours 23 minutes. Per month: 262.98 ÷ 12 gives about 21.91 min. Per day: 0.0005 × 1,440 = 0.72 min, roughly 43 seconds.

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Common mistakes

  • Entering the SLA as a fraction. Typing 0.999 means 0.999%, not 99.9%.
  • Assuming one more 9 means a small improvement. Going from 99.9% to 99.99% cuts the allowed downtime to a tenth.
  • Applying the yearly allowance to a single incident. The yearly total is shared by all outages in the period, and the monthly figure is the one that is usually measured.
  • Forgetting that planned maintenance is often excluded from the SLA, so real permitted downtime can be higher than the result.
  • Reading the result as hours. All three values are in minutes.

About this calculator

This calculator converts an uptime SLA percentage — like the famous “three nines” (99.9%) or “five nines” (99.999%) — into the actual allowed downtime per year, month, and day, since a service-level agreement's percentage figure alone is hard to reason about without translating it into real time. For example, 99.9% availability allows about 8 hours 45 minutes of downtime per year, while 99.99% allows only about 52 minutes.

DevOps and site-reliability engineers use this to set realistic monitoring alerts and error budgets, IT procurement teams and contract managers use it to compare what different vendors' SLA percentages actually guarantee, and cloud service providers use it when drafting or negotiating SLA terms with customers. Anyone evaluating a hosting, SaaS, or cloud contract uses this calculator to understand exactly how much outage the fine print permits.

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