Any saving if salary goes into mortgage account?

Hi,
If my wife and I both get our salaries (€4,200 after tax) paid into our mortgage account and we don't use the full €4,200 in a month I presume this would reduce our mortgage amount slightly?
Is the interest calculated on a daily basis on each month balance (daily I presume?)
I think for this you have to have a 'current account/offset mortgage'; is this correct? I'm with PTSB.

Cheers,
pa.

When you say you have it paid into your mortgage account do you just mean the account the mortgage payments come out of every month, if so then unless the mortgage was originally set up as an offset mortgage which I am not sure PTSB offered or not then there is no extra benefit from the credit in your account unless you earn interest on that account.

To the best of my knowledge only First Active (now Ulster Bank) and National Irish Bank offered current account / offset mortgages.

That is my recollection too, I have one of those First Active offset ones, have paid no interest in years. Yes I know I could possibly earn more in a fixed term account but I like it this way