Mortgage payment adjusts

The annual mortgage interest adjustment letter arrived. I have a 30 year mortgage that had a fixed rate for 5 years, then became subject to annual adjustments. As interests rates have been fairly low over the 14 years I've had the loan, I've never bothered to shell out the fees to refinance to a fixed rate.

Won't happen this year either: Previous index: 4.92%. Current index: 1.52%

Thanks to this and to regular additional payments on the principal, the monthly payment dropped 19%. I will, of course, adjust the additional payments on principal upward to keep my monthly payment the same as it has been.