Count your military spouse as fully employed if your spouse is not serving in a combat zone. According to the Internal Revenue Service (IRS) web page on military pay exclusion, any pay earned by a member of the Armed Forces in a non-combat zone is taxable and should be considered income. On a Form W-4, you can acknowledge your spouse's military income by marking a "0" or “1” in line “C” of the W-4.
Mark your spouse as having income of under $1,500 on the W-4 if your spouse has spent the year serving in a combat zone. According to the IRS regarding military pay exclusion, income earned during any month spent working in a combat zone is excluded from gross income. To mark your spouse as earning less than $1,500 on the W-4, put a “1” in line “B.”
Complete the “Two-Earners/Multiple Jobs Worksheet” only if your spouse is working outside of a combat zone. This section includes both your income and that of your military spouse, and helps your employer withhold the correct amount of taxes. If your spouse is in a combat zone, the income isn’t taxable, so you don’t need to include it on your W-4 to have additional taxes withheld.
Check the box regarding the Military Spouses Residency Relief Act if one is available for you on the form and you are a military spouse who has a permanent residence in another state. Some states, like Iowa and Connecticut, have added check boxes directly to their Form W-4. If that's the case in the state where you now are working, mark the box and enter the name of the state where your permanent residence is located.