What is the maximum amount of wages and self-employment income subject to the Social Security tax this year? What about Medicare taxes? How do they work?

Tom Herman from the Wall St. Journal writes the Answer:   First, let's focus on your Social Security taxes. The maximum amount of earnings subject to the Social Security tax for 2013 is $113,700, according to the Social Security Administration. That's up from $110,100 last year.

The government estimates about 163 million workers will pay Social Security taxes this year. Of those, nearly 10 million will pay higher taxes as a result of this increase in what the Social Security Administration calls the "taxable minimum." The taxable minimum amount reflects the increase in average wages.

On Medicare taxes: There is no limit on the amount of your income that is subject to Medicare taxes.

Now get ready for a new twist: Starting this year, many upper-income taxpayers have to pay an additional 0.9% Medicare tax on earned income above a certain threshold. The threshold generally is $200,000, but it's $250,000 for married couples who file joint returns.

Here is how the tax rates work (excluding the new 0.9% tax on high-income taxpayers): For employees, the Social Security tax rate is 6.2% on income under $113,700 through the end of this year. The Medicare tax rate is 1.45% of all earned income.

For employers, the amounts are the same: The Social Security tax rate is 6.2%, while the Medicare rate is 1.45%. For self-employed workers, the Social Security tax rate is 12.4% on income under $113,700 this year. The Medicare rate is 2.9%.

You can find more details on this subject on the Social Security Administration'swebsite and on the Internal Revenue Service's website.

Did you work for two or more employers last year? If so, make sure you didn't overpay your Social Security taxes. Tax pros say it's easy for many people, such as moonlighters or those who switched employers, to overlook this issue.

Add up the amounts that were withheld your paychecks. If the total amount last year was more than $4,624.40, claim a credit for the excess amount on your federal income-tax return. Put the excess amount on line 69 of Form 1040, or on line 41 or Form 1040A.

To fix errors or omissions on a federal income-tax return you've already filed, file Form 1040X, known as an "amended" return. File a separate Form 1040X for each year that needs to be amended, the IRS says.