The amount of your nontaxable combat pay should be shown on your Form W-2 Wage and Tax Statement, Box 12, with code "Q."
Per IRS Publication 3 Armed Forces' Tax Guide, on page 24:
For purposes of the earned income credit, earned income generally includes the following.
You can elect to include your nontaxable combat pay in earned income for the EIC. If you make the election, you must include in earned income all nontaxable combat pay you received. If you are filing a joint return and both you and your spouse received nontaxable combat pay, you can each make your own election. In other words, if one of you makes the election, the other one can also make it but doesn't have to.
The amount of your nontaxable combat pay should be shown on your Form W-2 in box 12 with code Q. Electing to include nontaxable combat pay in earned income may increase or decrease your EIC.
When figuring your earned income for purposes of the earned income credit, don't include any of these amounts.
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