How loan payments are calculated
Most installment loans are amortized: every payment is the same, but early payments are mostly interest and later ones mostly principal. The formula is P × i ÷ (1 − (1 + i)^−n), where i is the monthly rate and n the number of payments.
How to pay less interest
Choose a shorter term, shop for a lower APR, or make extra principal payments when your lender allows it.