If your mortgage company won’t let you do this, what my coworker said she does is has a separate account just for her mortgage. Every pay, she has half of her mortgage payment deposited into that account (you could also set up an auto transfer if you’re not able to split up your direct deposit), then she has the payment come out once a month. But since we get paid 26 times a year, she ends up with extra money in the account which she uses to make a principal payment at the end of the year. I’m thinking you wouldn’t save quite as much interest this way since you are waiting until end of year to make a lump sum payment, but it’s still something.