Tracker mortgage, overpayment and interests calculations

[jlbap27]

I have a tracker mortgage with PTSB at ECB + 1.1% (pretty high). Still 11.5 years to go.
Till now, I have been paying monthly and thought (after reading a lot) about fortnightly payment I could set it up to speed up my repayment years. However, when I contacted PTSB, I got various info. At the end, I got one person saying that my payment is only taken once a month and interests calculated daily on my principal and what is in their "arrears/prepayment"
I am very clueless with all these things.
So IF I put money regularly in the "arrears/prepayment", is it considered as Overpayment and how the interests are calculated? Will it help to reduce the remaining years I have left to pay off my mortgage?
If I build up money in the "arrears/prepayment" can it be used as Lump sum?

 

[cremeegg]

Interest is calculated as a percentage of the amount outstanding. Its not more complicated than that.

When you make a payment it reduces the amount outstanding.

The bank may not want to accept payments more than once a month, as it costs them something to process the payments.

 

[jlbap27]

Interest is calculated as a percentage of the amount outstanding. Its not more complicated than that.

So how do you calculate it then?
Of course, when a payment is made, it reduces the outstanding amount, that's why you make payment!