Hi,
This may seem like a strange question but say if you have 20K to spare. Does it make more sense to accelerate your mortgage repayments or simply knock the 20K directly off the mortgage?
Paying the €20K lump sum off the outstanding capital would yield the highest savings. If you keep the mortgage repayments at their pre-capital repayment level then the term will reduce too. See Karl Jeacle's mortgage calculator.