Claim too many withholding exemptions on the Form W-4 you file with your employer and you'll end up paying Uncle Sam interest and penalties in addition to the under-withheld taxes when you file your income tax return. Claim too few withholding exemptions and you'll end up lending Uncle Sam your money interest free when it could be working for you in an interest bearing account or investment. Here's how to tweak your withholding so it benefits YOU, not the government.