To calculate the uptime percentage, you must determine the ratio of the actual operational time to the total scheduled time and then convert that ratio to a percentage.

1. Actual Operational Time (Numerator): This is calculated by taking the total possible time the service was scheduled to be available and subtracting any time it was unavailable.

• (Maximum Available Minutes – Downtime in Minutes)

1. Total Scheduled Time (Denominator): This is the total time frame being measured.

• Maximum Available Minutes

1. Percentage Conversion (Multiplier): To express the resulting ratio (a decimal) as a percentage, you must multiply it by 100.

• 100

The complete formula is: $\text{Availability \%} = \frac{(\text{Total Time} - \text{Downtime})}{\text{Total Time}} \times 100$

Microsoft. (2023). Service Level Agreements (SLA) for Online Services. Microsoft Licensing Documents.Reference: While specific calculation formulas are detailed in individual service SLAs, the concept is standardized. The SLA defines "Monthly Uptime Percentage," which is universally calculated by taking the total minutes in a month, subtracting the minutes of "Downtime," and dividing by the total minutes in the month.Lyu, M. R. (2007). "Software Reliability Engineering: A Roadmap." In Future of Software Engineering (FOSE '07). IEEE Computer Society, pp. 153–170.DOI: https://doi.org/10.1109/FOSE.2007.25Reference: This paper discusses software reliability and availability. On page 162, Availability ($A(t)$) is defined in its simplified form as a ratio of uptime to total time: $A(t) = \frac{\text{Uptime}}{\text{Uptime} + \text{Downtime}}$. This is mathematically equivalent to the formula in the answer: $\frac{(\text{Total Time} - \text{Downtime})}{\text{Total Time}}$.Zio, E. (2009). "Reliability engineering: Old problems and new challenges." Reliability Engineering & System Safety, 94(2), pp. 125–141.DOI: https://doi.org/10.1016/j.ress.2008.06.002Reference: Section 2.1 defines availability as "the probability that the system is operational at a given time $t$." The practical, time-based calculation for this is consistently represented as the ratio of operational time (total time minus downtime) to the total time over a given interval.