How can I have a $64,000 capital gain and no tax on it?

[MinhT1]

This is possible if you are filing jointly and have taxable income of less than $94,050.

Long term capital gains are taxed at 0% if your taxable income is less than $47,025 for Single or MFS or less than $94,050 for MFJ..

However, long term capital gains are included in your taxable income for the calculation of these thresholds, and that part of long term gains which crosses over $47,025 (Single or MFS) or $94,050 (MFJ) is taxed at 15%.

Please read this IRS document for more information.