I would love to see the math of it saving years. Making an extra entire monthly payment a year by having the mortgage lender agree to accept bi-weekly payments saves less than 7 years in the examples I linked. Amortizations on mortgages are figured on the remaining balance at the time of payment and the interest rate. Making part of a payment half a month early will save a little (very little) interest assuming the lender has agreed to accept the payment and credit it in that way. Not enough to shave years off the mortgage.
In this example it saved one month over 30 years.
https://budgeting.thenest.com/making-semimonthly-payments-mortgage-save-money-23747.html
A semimonthly payment schedule won't save you much money. With this plan, you are making two payments per month instead of one, adding up to the equivalent of 12 full payments. By making semimonthly payments on a 30-year mortgage, you’ll pay off your loan in 29 years 11 months – only one month sooner than if you were to make monthly payments.
Consequently, you’ll save only the amount of one month’s worth of interest over the life of your loan. However, making half your regular mortgage payment every two weeks, or biweekly, will save you a bundle.
https://everythingfinanceblog.com/5455/the-advantages-of-a-semi-monthly-mortgage-payments.html
. When you only make one payment a month, the interest balance can continue to accrue over 30 or 31 days. With semi-monthly payments, the interest never accrues more than 15 days. For instance, if you have a mortgage for $200,000 at 5% interest for 30 years, you would pay $186,513.10 on a traditional mortgage that is paid once a month. However, if you pay on a semi-monthly basis, your overall interest paid over the life of the loan is $186,339.34, or
$173.76 less over 30 years.