capital gain - advice for someone new

[Tatyana Williams]

Dear BPs.

My husband is about to sell the home we live in with a potential capital gain. I understand that for a married couple $500K of capital gain is tax free. Question:

1. Is this a once in a lifetime "thing" or could it be repeated?

2. If hypothetically speaking there is more than 500K capital gain, then what is the tax rate on that amount?

3. Lastly, I apologize for a really dumb question but is a capital gain difference between what you bought the house for and what you sold it for?

Thank you, all, so much for your great help and advice