Why do I owe money on my taxes?

The tax which is withheld from each of your paychecks is only an estimation of the tax that you actually have to pay. The amount of tax withheld is reported on your form W-2.

When you file your tax return, if the amount of tax withheld is less than your tax liability, the difference is the tax that you have to pay with your tax return. On the contrary, if the amount withheld is greater than your tax liability, you'll receive a refund.

You can choose to increase the amount of tax withheld from each paycheck so that you do not have taxes due at tax time. To do this, you should file a new form W-4 with your employer.