Calculate simple interest and end balance based on the formula I = Prt or I = Prn. Learn the difference between simple and compound interest , and see examples and graphs. Use our free Monthly Interest Calculator to easily calculate your interest earnings or payments. Perfect for savings accounts, loans, and investments. Learn how to calculate the interest rate per month with simple and compound interest formulas. Use Codingindialab free tool for quick. Monthly interest can be calculated by converting the period and the interest rate into months . Divide the interest rate per annum by 12 to convert it into a monthly rate . Consider the number of months instead of the number of years as the duration.