Have Tax Questions? Ask a Tax Expert for Answers ASAP
Welcome to Just Answer,
If you ever have any doubt, you can just put 0. This allowance would withhold the most from you pay. You would get this back as a refund if you overpaid when you file your return.
If you don't to use zero, I have attached a worksheet from the IRS than can help. They also have a withholding calculator on their website, which is useful as well.
I hope this helps.