You spent the last 40 years fattening the U.S. Treasury thanks to those dang FICA taxes that came out of every paycheck. Now you're retiring and it's time to get your tax money back, free and clear, right?

Well, maybe; maybe not.

You certainly are entitled to the Social Security benefits your payroll taxes went toward. But the IRS also could take a bite out of those federal retirement checks.

Generally, if Social Security benefits are your only income, your benefits are not taxable. From the IRS's standpoint, Social Security benefits include monthly survivor and disability benefits; supplemental security income payments are not taxable.

But if you collect Social Security plus other income, as much as 85 percent of what Uncle Sam pays you could be subject to tax. To figure out just how much in taxes your Social Security might cost you, you'll have to do some calculating using the worksheet found in your 1040 or 1040A tax package.

If you discover that you will owe taxes on some of your Social Security benefits, there are two ways to deal with them. You can make estimated tax payments on the government check amounts. Or you can have federal income tax withheld from your benefits by completing Form W-4V, Voluntary Withholding Request, and filing it with the Social Security Administration.

This tax tip has more details on taxation of federal retirement benefits. And for more financial strategies as you count down to retirement, check out this collection of Bankrate articles.

-- Text by Kay Bell, illustrations by Brandy Kesl.