Doubt - SelfEmployement or SoleTrader - Earning Calculation

[venpad2008]

Hi,
My extn due is Jun. 2013
I am self employed, working as sub contractor from May 2012 – Apr 2013, registered with HMRC and received UTR number.
I am paying Class2 NI every month through my personal bank account, as direct debit.
I am waiting for Self Assessment tax return notice from HMRC, by April 2013.

I am planning to apply extn by mid of May 2013, when I read the general guidance (page 17, point no. 94), I doubt about earning calculation.

“The appropriate proportion of the net profit of the business (that is , after tax and outgoings) can therefore be counted as the gross salary”

Total salary before tax = 42000
Approx. tax calculation = 10000

Doubt: Can you please help me to find what is the "net profit of the business"? Is it 42000 or 32000 (after tax deduction).

note: there is no 'outgoings' (expenses).

Thanks for your effort.
-Ven