How to calculate the EMI - for loan purpose ?

A is the amount of the loan
r is the interest rate per interval. If you are paying 3% per year but paying monthly, it is .03/12.
n is the number of intervals. 360 months is you have a 30 year loan paying monthly.

P is the Principal amount of the loan

A is the Annuity, the EMI , the equal monthly instalment

n is the number of payments , 360 monthly payments in a 30 year loan payable monthly in arrears.

The formula equates the Principal to the net present value of the future payments by summing the geometric progression.