The monthly payment
A fixed-rate loan is paid off in equal monthly payments. Each month, interest is charged on what you still owe, at the yearly rate divided by 12; the rest of the payment comes off the balance. Early on most of the payment is interest; by the end almost all of it is paying down the loan. The formula is P × r ÷ (1 − (1 + r)^−n), where P is the amount borrowed, r the monthly rate and n the number of payments.
Paying extra
Anything paid on top of the payment comes straight off the balance, so every later month is charged less interest. Even a small extra amount each month cuts the total interest and the number of payments. Check that your lender applies extra payments to the principal and does not charge for paying early.
APR and what is left out
Put in the loan's APR. The schedule assumes a fixed rate, payments on time, and interest worked out monthly; fees added to the loan, a variable rate, or interest charged daily will make the real figures differ a little.
Questions
How is the payoff date worked out?
From the month of the first payment, counting one payment a month. With extra payments, the last payment is the month the balance reaches zero, and it may be smaller than the rest.
Is this a quote?
No. It is an estimate for planning. Your lender's figures are the ones that count.
Can I work out a mortgage?
Use the Mortgage Calculator, which adds property tax, insurance, PMI and HOA fees to the loan payment.