You can deduct insurance premiums if you pay them with after-tax money. If you take it as a personal deduction on schedule A it is subject to the 10% rule so your benefit may be reduced.
I'm pretty sure you can deduct the premiums directly as a schedule C expense (instead of a schedule A itemized deduction) even if you obtained the plan from someplace other than the small business marketplace. But someone else may correct me.
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If you pay the premiums with before-tax dollars (such as, they are deducted pre-tax from your pension) then you can't deduct them again.
