General
All of these day count conventions are calculated by taking as the numerator the actual number of days between the start and end of the period. The denominator is 360, 365 or 366 depending on the actual convention used.
Actual/360
The number of days in the period divided by 360.
Actual/365 Fixed
The number of days in the period divided by 365.
Actual/366
The number of days in the period divided by 366.