Dear Liz: I am trying to understand the capital gains tax exemption as it applies to the sale of a house. If I have no mortgage and I sell my house before I have lived in it for two of the previous five years that are now required for the exemption, is it based on the total selling price of the house or on the amount over what I paid for it? And what is the tax rate based on?

Answer: The home sale exemption can shelter from taxes up to $250,000 per owner ($500,000 for a couple) of capital gains from a home sale. If you don’t live in the home for at least two of the previous five years, you typically can’t use the exemption unless the sale was because of a change in employment, health problems that require you to move or an unforeseen circumstance that forced the sale.

The rules on these exceptions can get pretty tricky, so you’d need to discuss your situation with a tax pro. If you qualify, the amount of the exemption usually would be proportionate to the percentage of the two years that you actually lived in the home. If you sold after one year, for example, you might exempt up to $125,000 per owner.

Whether you have a mortgage does not affect the capital gains calculation. What matters is the difference between the price you get when you sell the house and the price you paid when you bought it.

From the sale price, you get to subtract any selling costs such as real estate commissions. From the purchase price, you can add in certain costs, such as home improvement expenses. What results after these adjustments is your capital gain for tax purposes.

If you have capital gains in excess of the exemption, you would pay long-term capital gains rates on that profit. Long-term capital gains are typically taxed at a 15% federal rate, although the highest-income taxpayers (those in the 39.6% bracket) may pay 20% and the lowest-income taxpayers (those in the 10% and 15% brackets, including taxable capital gains) pay a 0% rate.

States typically have additional taxes.