If you're paying an interest rate of say, 7.5% on a $100,000 loan and you can change your mortgage to another, which charges you 7% you'll be saving $31 per month.

That is $372 a year or $9,300 over a 25 year mortgage term. (If invested instead this could be worth considerably more). And that's only for one half of a percentage change.

The main thing to know is the cost of the penalties you will have to pay for giving up your old mortgage.

A quick call to your mortgage provider should tell you this. Just have your reference number to hand.

Similarly a quick call to an Independent Financial Adviser or the possible new mortgage provider will show you how much your new mortgage will cost.

It is easier to do it this way than with a calculator because there are so many variables involved.