If you claim 10 allowances on the W-4 form how can you calculate what your federal income tax withholding will be every weekly paycheck?

go to the IRS website or google and search for "payroll tax withholdings for employers"...the IRS puts out a table for your employer so that they know how much to take out of your paycheck with repect to your number of allowances.

If you are an employer trying to figure how much you must withhold from your employees, see Publication 15:

http://www.IRS.gov/pub/IRS-pdf/p15.pdf

and the updated tables in Publication 15-T:

http://www.IRS.gov/pub/IRS-pdf/p15t.pdf

If you just want to see how much will be deducted from your own pay, you can use the following calculator to determine how much tax will be deducted from your paycheck:

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

Remember that the amount of income tax deducted depends on how you fill out Form W-4 that you give to your employer. Properly doing so, and using the accompanying worksheets, is the best way to assure the right amount is withheld. IT IS NOT A FIXED OR SPECIFIC AMOUNT - YOU CONTROL IT...It is not the real amount of tax you owe. The real amount is calculated when you fill out your tax return at the end of the year. When you fill out and file your tax return, you will get a refund if too much was deducted or you will pay more if not enough was deducted. You want to have an amount paid in close to what you owe....and of course...any two people, even at the same job and salary, rarely have the sam tax situation and actually pay the same tax.