Take your adjustable gross income (What you were actually paid, minus all the deductions and exemptions you qualify for. Personal deduction/exemption, mortgage interest paid, property taxes, etcetera.) Imagine it's a big pile of money (or casino chips?) that you can divide into stacks. If you're single, take that pile and build your stacks in this order:
First stack: $7,825. Second stack: $24,025. Third stack: $45,250. Fourth stack: $83,750. Fifth stack: $188,850. The sixth stack is everything you have left. These stacks represent the six income tax brackets.
If you make $65,000 a year, and after your deductions, you have $56,000 left, you would have three stacks: $7,825, $24,025, and $24,150. (You make enough to build the first two stacks completely, but can only partially build the third stack.)
The tax rates for single filers are 10%, 15%, 25%, 28%, 33%, and 35%. This means you pay 10% of the money in the first stack, 15% of the money in the second stack, 25% of the third, and so on.
So for our $65K/$56K example, you would pay $782.50 + $3603.75 + $6037.50 = $10,426.75. This is your "tax liability". The tax withheld in your paycheck counts towards this. If you didn't have enough withheld, you wrote a check. If more than that was withheld, you got a refund check.
Yes, that's a nice chunk of change. I'm sure you'd like it to be smaller. You definitely don't want it to be larger.
Do you wonder how the Obama tax plan would affect you? Knock $500 off your tax liability. $9,926.75. That's the "Making Work Pay" tax credit. (If you were making more than $75,000, it would only be $250. If you made over $100K, you wouldn't qualify for it anymore.)
You've heard that the top tax rates will rise to 36% and 39.4%. Guess what? For this example, that doesn't affect you! That's the rates on the fifth and sixth stacks. It's an extra 3% of the fifth stack, and an extra 4.9% of the sixth stack. You have to have an AGI of more than $160,850 to start building the fifth stack! ($349,700 to start building the sixth stack.)
Keep this in mind: The Obama tax credits all have income ceilings. They are aimed at middle- and low-income earners.