What is the formula of ordinary interest?

The formula for ordinary interest, which calculates interest based on a 360-day year, is given by:

[ I = P \times r \times t ]

where ( I ) is the interest, ( P ) is the principal amount (the initial sum of money), ( r ) is the annual interest rate (expressed as a decimal), and ( t ) is the time in years. This formula assumes that interest is calculated on the basis of a 360-day year, typically used in banking and finance.