I know someone who has claimed 6 exemptions and has no kids. What would happen to them?

The withholding is a lot less for someone who is claiming exemptions and doesn't actually have the dependents. In most situations when they file a tax return they will end up owing the government money and they will have to pay it back. Other factors also count such as do they only do this a couple of times throughout the year, such as when they have worked a lot of overtime? If this is the case then their tax refund will be less but they will not owe any money. For an example my spouse worked over 100 hours of overtime and changed his status to M 9. He only done this twice for the year and it decreased his federal taxes by around 800.00 for the two pay periods. So it just depends on how often they claim the dependents.