Equal principal-and-interest (also called annuity repayment) means you pay the same total amount every month for the entire loan term. Each payment covers the accrued interest for that period plus a portion of the principal. Early payments are mostly interest; later payments are mostly principal.
Interest rate has a significant impact. Even a small increase in the annual rate raises the monthly payment and dramatically increases total interest paid over the life of the loan. For example, on a 30-year loan, a 1% rate increase can cost tens of thousands more in total interest.
This calculator uses the standard annuity formula and is suitable for mortgages, car loans, personal loans, and any other fixed-rate, fixed-term installment loan. It does not handle variable-rate loans or equal-principal (decreasing payment) repayment schedules.