If you had a job at any time during 2008 but didn't earn much money, you could qualify for one of the nation's most lucrative, and most frequently missed, tax breaks -- the earned income tax credit.

It is a tax break that can land a family with two children a refund of as much as $4,824 -- even when they paid no federal income tax. But about one-quarter of those who qualify don't claim the credit, the Internal Revenue Service says.

Some people miss it because they don't earn enough to be required to file a tax return, and you can't claim the credit unless you file. Others may be confused, thinking it is available only to those with children. The credit is considerably more valuable for parents, but childless workers can claim it too.

Here are some questions and answers about the credit.

What do you need to know to claim this credit? Who qualifies?

There are 20 factors that determine whether you qualify and how much you get. The main issues:

-- Your total income must be below $15,880 if you have no children, less than $36,995 if you have one qualifying child and not more than $41,464 if you have two or more qualifying children.

-- You must not be a dependent of another taxpayer.

-- If you have no qualifying children, you must be between the ages of 25 and 65.

-- You must be a U.S. citizen or a legal immigrant for the entire year.

-- You must have a valid Social Security number for yourself and any child claimed.

-- Your filing status may not be "married, filing separately."

-- You must have income from work, and unless you're in the military, your work must be in the United States.

-- You may not have more than $2,950 in investment income.

How much is this credit worth?

The maximum credit amount is $438 for those with no children, $2,917 for those with one qualifying child and $4,824 for those with two or more children.

Generally speaking, the largest credits go to people whose income is a little less than half of the maximum threshold for their filing status. You'd get the maximum break as a dual-income family, for instance, if you earned about $18,000 and had two children.

Which children qualify?

A dependent child claimed for this tax credit must meet age, relationship and residency tests. The simplest is the residency test, which requires that the child live with you for more than half the year in the U.S.

The relationship test demands that the child be dependent on you and be your son or daughter, stepchild or foster child, grandchild, brother or sister (including step-sibling), niece or nephew. Continued...