Self-employment tax deduction

[NSNM]

I am kind of puzzled as to how much to deduct for 1/2 SE tax on form 1040 for tax year 2011?

Is it exactly on-half of calculated social security (4.2%+6.2%) and medicare taxes
or
6.2% upto 106800 (employer portion) + 1.45 of taxable medicare income.

How any of you are calculating this deduction ?

Thank you all for any of your views and input.

NSNM

[BP.]

Check out TTB p. 5-24.

[DonPriebe]

The calculation of the "one-half" is now done on Schedule SE. Follow the form.