If I've only worked at my new job for 6 months in 2019, do I have to include my w2 for this new job for these 2019 taxes? Or can I wait until next year?

[xmasbaby0]

Every 2019 W-2 that you received must be reported on your tax return, even if they are for small amounts.  Remember that each one of those W-2’s has your Social Security number on it, and that income was reported to the IRS by the employer.  You do not want to get in trouble with the IRS for under-reporting your income.

ALL of your W-2’s must be entered on the SAME tax return.  After you enter the first one, you click Add Another W-2.

[Carl]

All income from all sources received in a tax year must be reported on one single tax return for that specific tax year. You don't get to choose otherwise.