There is no compounding of interest on mortgages (at least not in the U.S.)... That is to say the accrued interest is NOT added to the balance of the loan, meaning that you will not be paying interest on interest.
Interest is calculated, by day, on the outstanding balance. When you make your payment, ALL accrued interest is paid, then escrow and what's left over is applied to the principal balance.
The only loans (that I can think of at the moment) that actually use compound interest are revolving lines of credit (credit cards)... and... of course, student loans if you're ever foolish enough to accept a forbearance (not to be confused with a deferment).