A millennial couple paid off their mortgage 21 years early with a simple calculation anyone can use

Add that to your monthly mortgage payment," Marques told Insider by email. What you've done with this calculation is broken up an entire extra annual mortgage payment ($1,000) into 12 parts ($83 each), making them easier to tackle.That $1,083 puts $1,000 per month towards the mortgage principal (the amount borrowed), and interest (the cost of borrowing that money), plus an extra $83 to the principal. To save over time, your extra payment must go to the principal instead of the interest.Marques and Shyra took the strategy one step further by making this 1/12 payment bi-weekly, along with switching their mortgage payment to a bi-weekly schedule. That's the equivalent of more than two extra monthly payments.By continuing to pay down the principal and paying less in interest over the life of the loan, it's possible to cut years from a mortgage.