Industry standards for interest calculations

[Laurence K.]

Just wondering what parameters are standards in lending and loan calculation.

Is one year classed as 12 months or 52 weeks or 365 days, or is there an allowance for leap years by using 365 1/4 days.

Simple interest or compound interest ?

Using the PMT function in excel , the [type] argument can have the value 0 or 1, meaning:

0 - the payment is made at the end of the period;
1 - the payment is made at the beginning of the period.

Which of these is most commonly used ?