Oh I think I know what you're trying to say.
The earned income credit (not the child tax credit) works like a bell curve. So the more you make up to a point you'll get more of the EIC credit. You'll especially get more if your married and have up to three kids. Once you reach the highest point (somewhere in the $20,000 range for most people) it starts going back down.
The amount of income is adjusted gross income. So if you made say $10,000 but your adjusted gross income is $5000 then you'd get less of a tax credit. So you might not want to claim all those deductions.
I hope that makes sense.
Here's the URL to the EIC table. It takes a bit to load- but you can find your income and then see how much of a return you'd expect to get. Put in your deductions and see if it is actually worth it to claim them. OR talk to a tax preparer and they'll help you decide:
at 1:00 AM on Jan. 24, 2011