russ_watters said:
Its actually pretty easy: if you're in the $37-$80k bracket your marginal rate is 30% and the fica+med is 5.6%. Then add any flat state or local taxes and your 401k. Typical total would be around 45%.
Yes, definitely don't forget your other paycheck withholdings/payments (Insurance, 401k, Stock Purchase etc).
Unless you're extremely tight to start, you may be better off just seeing what your first pay check comes out to and extrapolate. That will likely be a bit more accurate than taking into account all of the little taxes, fees, etc at the appropriate rate.
eg: if you're clearing $1500 in your first check and you get paid twice a month, you would have $36k for the year in pocket.
If you do choose to computer your taxes, remember that the rate is marginal. Single tax rate for $34,001 – $82,400 is 25%. But... $8,376 – $34,000 is 15% and less is 10%. You'll also have a standard deduction of about 10k off the top, so your tax-liable income is probably 10k less than your yearly salary.
Presuming you fall into the bracket above you're really looking at:
8375*.10 + (34000-8375)*.15 + ([your income minus ~$10k std deduction] - 34000)*.25
So your real income tax rate at $34,002 is still in the low teens (just $2 are taxed at 25%, and the 8375 is at 10%).
http://en.wikipedia.org/wiki/US_Income_tax#Year_2010_income_brackets_and_tax_rates