How much will I owe on my house when I sell it?

This is great information to know.  When you take the amount you owe, the value of your house, and selling expenses, you will have a good idea of what funds you will have to work with on another house, or what you would have available for a line of credit, refinance, etc.  The difference between the estimated value of your house and the payoff of your mortgage is your equity and is considered part of your net worth.

To determine what you owe on your mortgage is a fairly straightforward calculation. Depending on the interest rate you obtained from your lender, and the length of your mortgage life, you will pay down your mortgage at a rate established by the two.  Each month you pay approximately 1/12 of the interest on the balance, with the rest of the payment made of principle - paying down what you owe.  While there may be taxes and insurance of various kinds, the part of the payment that matters is the principle.  You can see how as you pay down the balance of the loan, the 1/12 interest is charged to a lower and lower balance.  That is why so little of the principle is paid in the first few years and so much near the end of the loan.

I remember when Kelly and I closed on our house.  Among all the paperwork were several pages of the amortization of our mortgage.  In other words, we received a statement of the balance of our mortgage each month for the entire 30 years of our loan.  We could look at a particular date and see what the approximate payoff of our mortgage would be.

Now, you may be like me, and have no idea where that document is, but if you do, it is nice to know what you are going to owe in a couple of years so may want to put it in a place you can easily reference.

As an alternative to this paperwork, there are several on-line calculators designed just for answering this question.  I use Karl's mortgage calculator but there are many others, including lender websites and apps.  These are designed so you can enter in your interest rate, term and start date, then you are able to find out how much your principle will be at any given date.