You've planned for decades, saved your money and are ready for a comfortable retirement. You're plotting the perfect route for that cross-country trip, signing up for an art class you never had time for or getting standing tee times for 36 holes of golf a day.

In this tax tip: • Social Security excluded   • Potential tax preview   • Figuring your tax bill   • Paying throughout the year

Taxes certainly aren't on your retirement to-do list. But maybe they should be.

If you collect Social Security, some of it might be taxable depending on your total income and marital status. Retirees should have gotten Form SSA-1099 from the Social Security Administration at the end of January or early February.

The form will show your total benefits, but figuring out just how much is taxable requires putting pencil to paper or, if you're using tax software, fingers to keyboard.

Social Security alone is usually excluded
Generally, if Social Security is your only income, your benefits are not taxable, and you probably do not need to file a federal income tax return.

From the Internal Revenue Service's standpoint, Social Security benefits include monthly survivor and disability benefits, but not supplemental security income payments, which are not taxable.

But if you collect other income in addition to Social Security, you could owe taxes on at least a portion of your government benefits.

Potential tax preview
For a quick computation of your potential tax liability, add one-half of your Social Security benefits to all your other income.

In this calculation, you must also take into account any tax-exempt interest you earned, as well as exclusions from income such as savings bond interest, work-provided adoption benefits or foreign-earned income.

If this amount is greater than the base amount for your filing status, a part of your benefits will be taxable.

Base amounts for figuring possible tax liability on benefits are:

• $25,000 for single, head of household, or qualifying widow or widower with a dependent child. • $25,000 for married individuals filing separately and who did not live with their spouses at any time during the tax year. • $32,000 for married couples filing jointly. • Zero for married persons filing separately who lived together at any time during the tax year.

Figuring your tax bill
Once you determine that Uncle Sam is going to get a cut of your Social Security benefits, the next question to answer is precisely how big a bite he will take.

Generally, up to half of your benefits will be taxed if you exceed the base amounts. However, up to 85 percent of your benefits could be taxed if you are a single filer and the total of all your other income plus half of your Social Security checks exceeds $34,000, or $44,000 if you are married and file jointly.

You'll need to complete the work sheet found in your Form 1040 or 1040A instruction book, or in your tax software package, to find out the exact amount.

Paying throughout the year
If your government pension money is taxable, you can avoid estimated tax payments and minimize your tax bill next year by having federal income tax withheld from your benefits.

Simply complete Form W-4V, Voluntary Withholding Request, and file it with the Social Security Administration. You can choose to have 7 percent, 10 percent, 15 percent or 25 percent of your total benefit payment withheld.

If you subsequently decide you don't want the taxes withheld, you can file another W-4V to stop the withholding.

Additional information on the taxability of Social Security benefits is in IRS Publication 915, Social Security and Equivalent Railroad Retirement Benefits.

Freelance writer Kay Bell writes Bankrate's tax stories from her Austin, Texas, home. She also writes two tax blogs, Eye on the IRS for Bankrate and Don't Mess With Taxes, and is the author of the book "The Truth About Paying Fewer Taxes."