February 20, 2006
"I have an interest-only ARM on which I make principal payments as I am
able. My problem is that I don’t know exactly where I am in paying off
the mortgage. When will it pay off if I keep my principal payments at
their current level, or how much additional I would have to pay to pay
off by some specified period. Do you have anything that will help me?"
One of the nice things about a mortgage on which you make the
fully-amortizing payment is that you know that if you keep at it, your
balance will hit zero in the terminal month. When you take out an
interest-only (IO), in contrast, you can lose sight of where you are,
especially if the IO is an ARM on which the rate can change.
I have received so many letters about this that I finally bit the bullet
and developed an IO spreadsheet, which can be used for both fixed and
adjustable rate mortgages. This is it.
Keeping Track of Payments on
Interest-Only (IO) Mortgages
The spreadsheet allows you to see at a glance how a principal payment
impacts the balance, the interest payment in the following month, and
the fully amortizing payment. The last is important, because it is what
you are obliged to pay when the IO period ends.
Like all my spreadsheets, this one can be downloaded onto your computer
so you can maintain a permanent record close to home.