What it is
In a designated combat zone, enlisted pay and warrant officer pay is entirely excluded from federal income tax for each qualifying month, and officer pay is excluded up to a monthly cap. On the LES you see it as taxable wages dropping while your actual money stays the same or rises.
2026 rate
Full exclusion for enlisted, capped for officers.
What goes wrong
Even one day in the zone in a month qualifies the whole month. If you had qualifying days and your taxable wages did not drop, the exclusion was not applied and you are being overtaxed.