What if my matching 401(k) contributions were Roth contributions?

You should receive a Form 1099-R with Code G. This is the code for a rollover. Basically, the IRS treats the contribution as a rollover from a traditional 401(k) to a Roth 401(k). Your Form W-2 Box 1 should include the amount your company matched in your Roth 401(k).

This amount will be included on your tax return as income because it was a Roth contribution meaning that the taxes are paid now, and not paid when you withdraw in retirement.