To use a personal loan calculator, start by entering the loan amount you wish to borrow. Then, input the interest rate offered by the lender, followed by the loan term in months or years. The calculator will then provide you with an estimated monthly payment and the total cost of the loan over its term. Make sure to adjust any parameters to see how they affect your repayments. For the most accurate results, consider using a calculator from a reputable financial institution or compare offers from different providers.