You’d better use a good computer tax preparation program this year, or at least have a really good tax preparer. Otherwise, you’re gonna leave a big green bundle on the table.

There’s a new Schedule M that anybody with wages should file.

It allows you to claim the “Making Work Pay” credit of up to $400 ($800 on a joint return). That’s another $400 (or $800 for couples) right back in your pocket.

• Bing: Tax credits for 2009

You get a cash-back of 6.2% of the wages paid, with the above caps. If you adjusted gross income is more than $75,000 ($150,000 on a joint return), your credit is reduced by 2% of the excess.

So, if my wife, Barbara, and I have an adjusted gross income of $190,000, our $800 credit is reduced by 2% of $40,000, and we get “buptkis.”

(“Buptkis” is a technical tax term that means we get no credit)

Now, don’t get too excited.

When the Making Work Pay credit was passed by Congress, our financial idiot savants wanted to get the cash to you as quickly as possible. So, they provided for a change in the amount your employer withheld from each paycheck. In effect, Congress gave you the credit last year when it took less in withholding.

If the credit matches the reduction in withholding, there should be no change in what you would owe Uncle Sam.

But, if you don’t claim the credit, your reduced withholding could have you owing the IRS as much as an additional $800.

If you have no earned income but are receiving Social Security, SSI railroad retirement, or veteran disability compensation benefits, your credit is $250. A retired federal employee also qualifies for the $250 credit ($500 on a joint return if both spouses are eligible).

Both the Social Security and retired government employee benefits are one-shot deals for 2009. The regular Making Work Pay credit is good for 2009 and 2010.

But you’ve got to file the new Schedule M.

Related reading:

• 8 types of income the IRS can't touch
• The 19 most-overlooked tax deductions
• 7 easy steps to an early tax refund