Whether you have to file a federal income tax return depends on several factors, including your age and income. When it comes to state returns, however, there isn't a simple answer, because the laws vary depending on the state in which you live. That said, there are some general guidelines to follow.

Take What's Yours

Generally, even if you don't owe any state income tax, it can be a good idea to file a return. If your state tax withholding has resulted in an overpayment, it's silly not to get a refund -- that's your money, not the state's. Even if you aren't entitled to a refund, though, sometimes there can be refundable credits you can take advantage of, and doing so basically amounts to getting free money.

How Much of Your Income Is Taxable?

Most states allow a personal exemption, so if your income falls below that amount, or if your state withholding is sufficient to cover your taxes, you won't have to file. Some states -- Pennsylvania, for example -- have no personal exemption, so every dollar is taxable, making it more likely that you'll have to file. The best advice, however, is to check with a tax professional familiar with your state's laws.