My ex-husband wants to buy me out of my half of our house. The property is appraised at $1,800,000. After deducting commission, estimated repairs, paying off LOC, and half the mortgage, the net is approx $240,000. How is capital gains calculated and will I have to pay it?

You may NOT have any tax obligation.

What did you and your ex-husband PAY for the house?

The commission is a cost of sale, as are the closing costs and some repairs. What is LOC?

It depends. But before getting into details, you may be eligible to avoid capital gains entirely. Have you lived in the home as your primary residence (ie it's not a rental property or a vacation home) for at least two of the last five years? If so then you do not have to pay any capital gains, as you would qualify for an exclusion from capital gains on the sale of the house up to $250K (assuming you will file your taxes as single). If it wasn't your primary residence, then you will have to tell us the size of the down payment you made when you bought the house.