A repayment loan is paid off in equal monthly instalments. Each payment first covers the interest on what you still owe, and the rest reduces the balance, so early payments are mostly interest and late ones mostly principal. Mortgages, car loans and most personal loans work this way; this is the same calculation as the EMI calculator, in the currency you choose.
The formula. The payment is P × r × (1 + r)^n ÷ ((1 + r)^n − 1), where P is the amount borrowed, r the monthly rate (the annual rate ÷ 12 ÷ 100) and n the number of months. For $250,000 at 6.5% over 30 years, r is 0.5417% and n is 360, which gives $1,580.17 a month. Over the term that is $568,861, of which $318,861 is interest: more than the loan itself.
Extra payments. Money paid on top of the instalment goes straight to the balance, so it stops earning interest for the rest of the term. On that same loan, an extra $100 a month repays it in 25 years 4 months instead of 30 and saves about $58,860 of interest. The earlier in the term you pay extra, the more it saves; check first that your lender allows overpayments without a fee.
What it leaves out. The payment here is principal and interest only. A mortgage payment often also carries property tax, insurance and fees, and an adjustable-rate loan changes its payment when the rate resets. Rates are nominal annual rates compounded monthly, the way lenders quote them.