There are many formula for calculating compound interest by the month o
by the day etc.
The calculation for simple interest is the amount of loan outstandin
times the interest rate for the period, which, for a 10% rate charge
monthly would give you
Loan outstanding * 10 / 1200
However, you might need to check the law in your country, and the
ensure that no interest is charged on any previous interest debited.
This could occur if a payment were not received for a period, or if
payment of less than the interest for the period was received.
