When I make an overpayment, it sits in a seperate "overpayment" account the bank has. I can see the balance remaining on my mortgage on my online account and it's the net difference between whats left and what I've overpaid, but until I apply that overpayment against the capital remaining then the interest charged is still on the full balance remaining.
ie :
Mortgage - 20k
Overpayments - 5k
Remaining balance shown - 15k
Interest charged on - 20k
Hmm interesting, mine doesn't work that way. As i mentioned in a previous post the overpayment is combined with the fixed monthly payment. Once that comes out of the account on date X (usually 1st/2nd of the month) the balance is reduced by fixed amount + overpayment. At the end of the month the lender then works out the interest based on the balance after fixed amount + overpayment has been paid.
So based on that it would seem the overpayment is going towards the capital rather than the interest. As the interest is only worked out on the new balance after the overpayment is made.