This is known as a partial prepayment. The extra money may be applied assuming your loan is current and has the standard application requirements, (please check your Note, Mortgage and any applicable Riders for details) any amount over and above the regular payment amount will be applied first to any outstanding charges (late fees or interest) and then to principal. Also, if your Note has a prepayment fee, the extra monies sent could trigger that fee. Please check your note to verify there is no prepayment fee before sending extra money.