Didn't get a stimulus check? Think you deserve more than you got? Got one but think it's taxable? Or do you have a very limited memory and have no earthly clue what a "recovery rebate credit" might be? (A credit for people who discovered their 2007 rebate checks in the bottom of their recycling bins, perhaps?) Chances are, you're one of a whopping 15% of tax filers so far this year making an error on your return.

If you're preparing a paper return, check out Line 70 of Form 1040, Line 42 of Form 1040A or Line 9 of Form 1040EZ. The number on that line is probably zero (or you can leave it blank). If you make an error on that line and are owed a refund, it could delay the receipt of your money by a week or more, so you'll want to be careful.

Here's who might deserve a recovery rebate credit -- in other words, a tax credit equal to the stimulus check you should have received -- which is, surprisingly, calculated based either on 2007 or 2008 income (whichever gets you more stimulated, as it were):

• Those who didn't receive a stimulus check, or received a partial one, due to having income above $75,000 for single filers and $150,000 for married-filing-jointly folks. If your income in 2008 was a lot lower than 2007, you could deserve a rebate.
• Those who had a baby or adopted a child during 2008 (assuming your income is beneath the threshold).
• Those who didn't file taxes in 2007.
  
• Those who were claimed as a dependent in 2007, but not in 2008.

If you can't for the life of you remember how much you received, there are a bunch of ways to find out. You should have received "Notice 1378" from the IRS (it's a letter, not a form like the W2). Or go to the "How Much Was My Stimulus Payment?" tool on the IRS web site, or call 866-234-2942. You'll need your social security number, filing status, and number of exemptions from your 2007 tax return (Form 1040).

Finally, whatever you do, don't enter the amount of the economic stimulus check you received anywhere on your 1040 or other tax forms (you can enter it in the worksheet on the instructions, but you won't include that page in your filings). That'll cause an error. If you're using tax software, of course, you'll need to enter the amount you received (from the Notice 1378, if you have it), and the software will check for you if you deserve anything more.