How do i make calculations within my matrix?

How do i make calculations within my matrix? 

We have a form calculation widget. However, To my knowledge this is not yet compatible with the matrix field. Which means that if you want to create a Matrix with Calcuations then you have use the form's source code and build your own custom script to work like that if you have the knowledge to do so but please note that this may be a bit difficult to manipulate.

As far as I know we have plans to enable calculations on the Matrix Field but it is not yet ready for release so hopefully soon though I cannot promise as to when.