Cost basis

[jeff172]

If I do not enter a cost basis for stocks I sold I get a refund which is a credit for my premiums paid to health care marketplace. If  I enter a cost basis it lowers my actual income, but completley wipes out my credit/refund for healthcare premiums. Why is this?

[DawnC]

Your income must be near the cut-off point for the Premium Tax Credit.   The PTC is based on your annual income, family size, and zip code.  PTC Q&A   Look at Form 8962 to see how the allowable credit amount was calculated.  

#30.  When you complete your tax return, you will figure your credit and compare it to the amount of APTC on Form 8962.  If your actual allowable credit on your return is less than your APTC, called excess APTC, the difference, subject to certain repayment caps, will be subtracted from your refund or added to your balance due.  If your actual allowable credit is more than your APTC, the difference will be added to your refund or subtracted from your balance due.