But not every one of your $50,000 bills is taxed at 25 percent. The progressivity of the tax system means you pay more than one tax rate on your income.

"Progressivity means the more you earn, the more you pay," says LeValley-Cocovinis. "You can have a progressive flat rate and just start taxing at higher income levels. We have brackets, so when you earn more income, the higher amount will be taxed at higher rates."

The first portion of every individual's earnings is taxed at the lowest, 10-percent, rate. The subsequent rates start applying when your income hits a set level for your filing status. The tax rate you pay on your last dollar, that 50,000th one in our example, is your marginal tax rate, 25 percent in this case.

That's why you can't simply say, "I made $50,000 and am in the 25-percent bracket, so I owe $12,500." A look at the current tax table will show your bill actually is much less: $8,930.

5. Itemizing isn't always necessary 

But there are some tax breaks you can claim without having to itemize.

They are found at the bottom of the first page of both the 1040A and 1040 forms. Technically, they are adjustments to your income and are items you can claim to arrive at your adjusted gross income discussed in lesson No. 3.

Their popular name is above-the-line deductions, because they are located on the forms just above the line (No. 37 on the 1040 and No. 21 on the 1040A) where you enter your adjusted gross income.

Several adjustments are found on the 1040A. About a dozen can be claimed on the 1040. Unlike some of the deductions found on Schedule A, you don't face thresholds, such as the limits on itemized medical or miscellaneous expenses. You will, however, have to complete some worksheets and additional forms to claim these breaks in most cases.

You can take any above-the-line deductions you qualify for, regardless of whether you plan to claim the standard deduction or itemize to get even more breaks. So take a few minutes to look over the 1040A and 1040 forms to see if any of these breaks can help you.

6. Credits are better than deductions 

A deduction helps reduce your amount of taxable income. A credit directly reduces your tax bill.

Say you and your spouse use itemized deductions to get your taxable income to $40,000. When you file your joint return, you'll owe $5,221 to the IRS. You had a combined $4,000 withheld during the year, so you still owe $1,221.

But because you have a qualifying child, you can claim the $1,000 child tax credit. This will take your bill down to $221. And the amount you paid for care of your child while you both worked entitles you to a $200 credit. Thanks to these two credits, you only have to write a $21 check to the IRS.

People who don't understand the difference between a credit and deduction sometimes choose the tax break that offers the larger dollar amount. That could be a costly mistake.