Currently, most banks calculate the monthly payments on loans and mortgages inaccurately, using the traditional formula. This site aims to report that there is a correct way to calculate the interest, which is not usually applied.
To calculate the quota of your mortgage or loan along with its amortization schedule using the exact and approximated formula you can use the following calculator from a web browser:
If you prefer, you can download mobile applications to have them always available:
You can also download a spreadsheet that has calculations and a comparative graph that shows the difference between applying either formula.