Below is an extract from an IRS document which can be read in its entirety at this link:
https://www.irs.gov/taxtopics/tc409.html
Some or all net capital gain may be taxed at 0% if you're
in the 10% or 15% ordinary income tax brackets. However, a 20% tax
rate on net capital gain applies to the extent that a taxpayer's taxable
income exceeds the thresholds set for the 39.6% ordinary tax rate
($415,050 for single; $466,950 for married filing jointly or qualifying
widow(er); $441,000 for head of household, and $233,475 for married
filing separately).
There are a few other exceptions where capital gains may be taxed
at rates greater than 15%:
- The taxable part of a gain from selling section 1202 qualified
small business stock is taxed at a maximum 28% rate.
- Net capital gains from selling collectibles (such as coins or
art) are taxed at a maximum 28% rate.
- The portion of any unrecaptured section 1250 gain from selling
section 1250 real property is taxed at a maximum 25% rate.
Note:
Net short-term capital gains are subject to taxation as ordinary
income at graduated tax rates.