Any extra money paid should automatically go to principal.
An advantage of making payments early is that it reduces the tota1 number of payments more than extra payments later. A downside is that future payments will contain less interest and tax deduction. If you pay down enough, you could refinance and get a lower payment and start the process over again. This has the advantage of being able to handle the mortgage payment if your income declines.
They really should teach compound interest in high school.
If you can use Excel, know your interest rate and balance, you should be able to run through various scenarios. The interest rate is normally a nominal monthly rate (divide the rate by 12 and apply it to the outstanding balance yields the interest for the month. The remainder of the payment is for principle, taxes, and insurance. (Your mortgage company can give you the monthly expenses. They should give you a payout schedule)
BEST TO DICTATE THAT ON YOUR PAYMENT.
NOT THE BRIGHTEST ARE WORKING AT BANKS, ETC.