Employer contributions to a 401(k) are tax-deferred, meaning you do not pay taxes on their contributions until you withdraw the funds. The same is true for your own contributions to the 401(k). Your W2 form that the employer will send you each year will show your 401(k) contributions in box 12 as code D. The same amount should will be subtracted from your taxable income on the W2 box 1, meaning your taxable income will be reduced by your own 401(k) contributions. Employer contributions are generally not refected on form W2, but should appear on your 401(k) statement.
