If you sold business assets during the year — and that may include a part of your home if you were depreciating it as a home office — you need to complete and file Form 4797. On the bright side, this form usually offers a helping hand to taxpayers because net losses are treated as "ordinary losses", meaning they can generally be fully deducted while gains are treated as "capital gains", which may be taxed at a preferential rate. If you're affected, go through the Interview for this topic.