Service Availability Calculation

Service Availability % = [(TM – SM – DM)/(TM – SM)] * 100
Where:
TM = Total Minutes in the calendar month (i.e.: #days*24hrs*60mins)
SM = Scheduled Maintenance Time (in minutes)
DM = Unscheduled Downtime.

Eg:
Scheduled Maintenance - 10 mintues in a month
Downtime: 5 minutes in a month
(43200 - 10 - 5) / (43200 - 10) = 99.98%