If I owned a second home and held for more than five yrs and the appreciation was 500,000 what would the tax bill be?

Did you ever rent it out?

No exclusion, since this was not your primary residence.

https://www.fool.com/retirement/2016/12/11/long-term-capital-gains-tax-rates-in-2017.aspx

http://fairmark.com/general-taxation/reference-room/2017-tax-rate-schedules/

This can trigger the NIT and AMT as well.

https://www.irs.gov/newsroom/net-investment-income-tax-faqs

http://www.fool.com/answers/faq/capital-gains-affect-amt/

Also remember State taxes.

Of course, all this assumes no 2017 Federal tax law changes.