Some people make it a goal to pay off their mortgage early. In order to do this, you have to make extra principal payments.
If you make a large principal payment, you can usually request that your lender “recast” your mortgage. This means they will recalculate your monthly payment using the same interest rate and amount of time left but with the lower principal balance. This results in a lower payment for the remaining life of the loan.
If you are making large principal payments with some time in-between them, contact your lender to see if they will recast your mortgage!