Retired with $0 income and my wife's income is $20K which will put me in the LT cap gain rate 0%. If I take $100K in capital gains will I pay 0% capital gains or 15%?

[tagteam]

It depends, but at least a portion of the gain, assuming it is long-term, will be taxed at 15%.

For a more accurate estimate, use TaxCaster --> https://turbotax.intuit.com/tax-tools/calculators/taxcaster/

[TomYoung]

Assuming you are filling as Married/Joint then the LT capital gains will be taxed at 0% up to the point where your taxable income - after deductions - reaches $78,750.  LT capital gains after that get taxed at 15%

[Critter]

If you can ... sell a portion now and more later in the next tax year to keep in the 0% bracket ... tax plan well.

[Critter]

Or if you have some losers in the portfolio you can sell them to offset some of the gains to keep you in the 0% bracket.