Why are my HSA contributions shown in Box 12 of my W-2 not showing up as a deduction on my tax return?

If the Health Savings Account contributions are shown in Box 12 of your W-2, your W-2 Box 1 wages have already been reduced by the HSA contributions shown in Box 12. You do not get an additional deduction on Schedule 1, Line 13 for the HSA Contribution Deduction.