But I am hooked on semantics. Caren meant semi-monthly OR bi-weekly.
Splitting the interest payment in half and paying it twice a month would do nothing but annoy the mortgage servicer. It would result in no additional principal paydown.
Splitting the payment in half, then paying it every two weeks would eventually result in a month in which 3 payments were made due to the fact that a month is 30 or 31 days 11 out of the 12 months.
There is only one month that equals four weeks. (but none next year)
What it does not make sense to do is to pay $395 (or more) for a computer program to do what a simple 99 cent calendar and a quick visit or phone call to your payroll office can do which is tell you what month you will have three paycehcks.
If you are paid biweekly, and are paid about the same amount every payday, you could make an extra principal payment in those two months a year that you get paid 3 times in the same month.
If you are not paid bi-weekly, then the idea makes very little sense.
It makes more sense to pay additional principal when you have a little extra money that you will not need to ever see until you sell your home or pay it off.
It probably makes much more sense to put that money into a Roth or traditional IRA or a liquid investment that you can acess in an emergency.