How much should you estimate off per paycheck for taxes?

First use this calculator to figure out what to put on your Form W-4:

http://www.irs.gov/individuals/article/0,,id=96196,00.html

Then use this calculator to find out how much will be withheld from each paycheck:

http://www.paycheckcity.com/NetPayCalc/netpaycalculator.asp