7/1 ARM loan allows me to treat it as 7 years fixed loan if I pay n$ monthly.
for 30 years fixed loan, if I pay n$, I believe n-m$ will go to the principle. Let's say I paid n$ for this month. I pay m$ next months. How does my mortgage holder (the bank) spilt the principle and interest among m$? Does it charge the interest based the original schedule or charge less interest since I've reduced the balance by n-m$?
From your answer, you believed that the bank will compute the interest based on the balance each month. I asked my bank and they just told me that I can pay the loan off early by paying extra. They do not know the detail.