Unless you are actually deployed to an actual designated Combat zone...little to none. Everything except BAS/BAH and traditional TSP contributions are federally taxed.
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If you are deployed to a designated combat zone, the Combat pay you receive will be deducted from box 1 on that year's W-2 form, and that amount removed will be noted in box 12 with a code "Q". And you get an extension to file and pay taxes until after you return.
Extension of deadlines — Combat zone service | Internal Revenue Service
(But, if you delay filing and return from a Combat area late in 2025, TTX "Online" software cannot be used to file after ~15 October)
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Being deployed to a hazardous duty area is not the same as a designated Combat zone.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
