Maximum number of Allowances in W-4 Tax form?

If you end up underpaying, you can face penalties and taxes, so be careful. Fill out the W-4, filling in the allowances to the max. Generally I urge people to claim fewer allowances than the max, but if your income remains steady, your filing status is steady and you are getting larger and larger refunds, you should change your W-4. Since we're more than halfway through the year, you should be OK.