September 18, 2006, Revised April 29, 2008
It always pays to pay a simple interest mortgage early.
"I found that if I paid early one month and made the next payment on the
due date, the interest payment went up. So does it really pay to pay
early?"
Yes, on a simple interest mortgage, it always pays to pay early.
To convince you, I used my spreadsheet
Monitoring Amortization of a Simple Interest Loan to perform an
experiment that mirrored your case. Using a $100,000 30-year loan at 6%,
I first made the scheduled payment on days 31 and 62. The balance on day
62, reflecting the effects of both payments, was $99,819.60. Then I did
it again, except that in this case I made the payments on days 30 and
62. The balance in month 62 was $99,819.50, or $.10 less.
A dime is not a lot of money, but it reflects only one early payment,
early by only one month. Over time, the savings grow, the more so as
more payments are made early. If you pay every 30 days over the life of
the loan, there is a significant shortening of term. See
Amortizing a Simple
Interest Mortgage.