Profits and disposable income

[Rob Cussons]

Apologies, this may well be a stupid question, but I'm going to ask it
anyway!

I'm trying to understand what disposable income I have that could be put
towards an increased mortgage as part of a new house purchase. The simplest
way for me to see that, I think, is what is my disposable income month by
month. From what I understand, that disposable income is nothing by the net
profit = income - expenses by month. Please can someone tell me if this is
correct?

Thanks!