Are capital gains included in worldwide income?

Yes, capital gains are included in your worldwide income for US tax purposes.

Capital gains, gift, real estate, and inheritance taxes all apply to US citizens and Green Card holders regardless of where they were located. You will also be taxed on any income from dividends or investments overseas and may face increased reporting requirements on foreign mutual funds or investment vehicles. There may also be different tax rules and exceptions for each type of investment, so we suggest you seek expat tax advice regarding any capital gains you expect to receive in a given tax year.