Unless you are involved in Chemistry in some way or another the term half life probably isn't in your vocabulary. I would have loved to get rid of the term but because I did so poorly in that subject, it sticks around like unwanted company. (Side note: my brother was a professor of chemistry - it didn't help). I finally have found a way to use this term in a helpful manner that illustrates the basis of mortgage loans: the time use of money.

When you borrow money on any loan, including a mortgage loan, you always pay back the amount you borrow plus a little extra (or a lot extra) which is the interest on the money.I often get the feeling that people don't understand how mortgage loans work and think there is some magical formula for the paying back of the money. Most people don't even realize we use simple interest in our loans, not compound interest or dutch interest or anything else.

So the easiest way to show people how the loans work is to demonstrate the half life of the loan: when half of the loan is paid back. It tends to make people wonder what they have been doing. I noticed at a young age that a lender I had a loan with was always offering to extend the loan instead of raising the payment on my variable interest rate loan. I quickly realized that I would have to work this side of forever to get the loan paid off. On the other hand, I once took out a fixed second and sold the house in about a year and a half later. I found that I paid off as much on the smaller second in a year and a half (it was a 15 year loan) than I had paid off on my 30 year first in the four years I had that loan.

If you didn't have the privilege of learning at the "school of hard knocks" as I did then you might find the following explanation of half life quite interesting.

A 15 year fixed will be half paid off in approx. 10 years

A 20 year fixed will be half paid off in approx. 13 years.

A 30 year fixed will be half paid off in approx. 20 years

A 40 year fixed will be half paid off in approx. 30 years

(Different interest rates can change the pay back time)

Can you see the pattern? Most people would say they would like to just pay the second half of the loan which of course you can by taking a shorter amortization.

The real key to paying off your loan in a reasonable time without an enormous amount of interest is to pay it off in 20 years or less.