Fixed-rate loan, monthly payments. Everything runs in your browser; nothing you type is sent anywhere.
Formula.payment = P × r / (1 − (1 + r)−n), where P is the amount borrowed, r is the yearly rate ÷ 12 and n is the number of months. At 0% the payment is P ÷ n. The schedule rounds each month to the cent, so its interest total can differ from the exact formula by a few cents. Both are shown. The last payment absorbs the rounding.
Example check: $15,000 at 4% over 70 months gives $240.61 a month and $1,842.87 interest by the exact formula ($1,842.89 on the cent-rounded schedule). An earlier stored answer of $240.49 / $1,834.33 was slightly off. This is a math tool, not financial advice; lenders may compute days and fees differently.