What does it go to if it doesn't go to principal? That seems really odd to me as any extra payment I make comes straight off the balance owing. I am in Australia if that makes a difference.
My bank (WF) applies 100% of extra payment to principal -- unless the "extra" exceeds the entire amount of the monthly payment. Here are examples:
Assume monthly mortgage payment = $2000
ex1: Pay $2001-$3999. Bank uses $2000 toward PITI as usual, and uses the extra $1-$1999 toward Principal.
ex2: Pay $4000. Bank uses $2000 toward PITI as usual, and uses the extra $2000 toward the following month's payment. No decrease in interest owed, you've just paid one month in advance. You either have to NOT pay the next month, or call the bank to get them to correct it.
ex3: Pay >$4000. Bank uses $2000 toward PITI as usual, and uses the extra $2000 toward the following month's payment, and uses any amount over $4000 to go to principal.
For whatever reason, there is no way for me to tell my bank that I want ALL extra payments, EVERY time, to go straight to principal. I have to call to tell them every month. So I've given up on that. Now I just pay $3999 automatically and if I want to make an extra payment, I save it up and walk into the bank when it's worth my while to do it.