My Fiancé received a sign on bonus for 5K before she started work in June. It was not put on her W2. The tax form she did receive did not show that any taxes were taken out.

Should she just add this amount to her wages box? Or where should she declare this as it has not already been taxed.

She lives and works in Illinois.

Tell her to go to her boss and have them correct the W-2 and issue her a W-2C. That is the BEST way to handle it.

Otherwise, she can claim it on Line #21 (Other Income), but she best be ready to explain that entry.

It is NOT self-employment income, so Schedule C is NOT the answer.