https://www.irs.gov/pub/irs-pdf/p544.pdf
Exclusion of gain. You may be able to exclude from your gross income 50% of your gain
from the sale or exchange of qualified small
business stock you held more than 5 years. The
exclusion can be up to 75% for stock acquired
after February 17, 2009, and up to 100% for
stock acquired after September 27, 2010. The exclusion can be up to 60% for certain empowerment zone business stock.
Your gain from the stock of any one issuer
that is eligible for the exclusion is limited to the
greater of the following amounts.
• Ten times your basis in all qualified stock
of the issuer you sold or exchanged during
the year.
• $10 million ($5 million for married individuals filing separately) minus the gain from
the stock of the same issuer you used to
figure your exclusion in earlier years.
More information. For more information on
sales of small business stock, see chapter 4 of
Pub. 550. See the Instructions for Schedule D
(Form 1040) and the Instructions for Form 8949
for information on how to report the gain.