The basis of an interest calculation is a convention whereby an interest amount is calculated from the principal, expressed in units of a specified currency, and a percentage, and an agreed start and end date There are many conventions, including
(1) SemiAnnual
C = P.R / 2
Commonly used for bond coupon calculation
(2) Actual 365
C = P.R. (EndDate - Startdate)/365
where start and end dates are expressed as Julian Dates
Commonly used in the sterling markets and in for "Commonwealth"currencies
(3) 30 / 360