A mortgage payment is driven by three numbers: how much you borrow, the interest rate, and the term. Those combine into a fixed monthly figure — but the split between interest and principal, and the total you pay over the years, are where the real story is.
The three inputs
A larger loan or a higher rate raises the payment, as you would expect. The term is the sneaky one: a longer term lowers the monthly payment, which feels good, but you pay for many more years, so the total interest can rise dramatically even though each payment is smaller.
How to estimate yours
- Open the mortgage calculator.
- Enter the loan amount, interest rate and term in years.
- Read the monthly payment and, just as importantly, the total interest over the life of the loan.
Early payments are mostly interest
In the first years, most of each payment goes to interest and only a little to the balance; that flips over time. This is why overpaying early — even a little — saves a surprising amount, because it cuts the balance that all future interest is charged on.
Compare the same loan over 25 and 30 years. The monthly saving looks attractive, but check the total interest column — the longer term often costs tens of thousands more.