Please someone help me with these numbers and tax things my brain is melting....melting....

[colditz]

I have worked out how much money from Dp's job we got after tax by checking our bank statements. How can I work out how much that would have been before tax?

Depends how much tax he pays, Colditz. If he pays 25%, divide your net amount by 3 and add the result on. If he pays 40% it's a bit more complicated but will explain if you need me to.

Does he have a P11d (I think it's called)? Summary from employer showing gross and net pay.

I think it is a P60 that you get each year from your employer with the gross and net pay (issued about June each year). Doesn't your DP have a payslip?!