Ok sorry if you cant follow, an example might be easier;
Example
Loan €200,000 over 35 years equals repayments of €1,004pm. Cost of loan is €223,934.56
Loan €200,000 over 30 years equals repayments of €1,073pm. Cost of loan is €186,513.24
So you decide to take a loan of €200,000 over 35 years, repayments are €1,004pm plus you ask the bank to reduce the capital of the loan by the difference of the monthly repayments between 30 & 35years, in this case, €69.31 and the cost of the loan is €184,153.00
So by prepayment you would save €2,360.24 over the life of your mortgage if you took out a 35year mortgage and paid the monthly repayments equal to what you would pay if you took a mortgage for the same amount over 30 years?