Karl Jeacle calculator

[Thrifty1]

I have this calculator yet when i key in the mortgage details along with the interest rate im paying the amount of the repayment is different to that im actually paying. The amount the calculator gives is less than the actual.
What would be causing this difference?
Thanks.

 

[Robin Banks]

Eh, you'll have to give a bit more information than that.. How big is the difference?