After the death of my spouse, I sold property that I had owned jointly with her. What’s my basis?

Assuming your spouse died after 1981 and that your spouse was a U.S. citizen, you owned a “qualified joint interest” with your spouse. As such, your basis is 50% of the date-of-death fair market value of the property, plus one half of the original cost of the property. By the numbers, this would mean that if property purchased years ago for $100,000 was worth $300,000 when your spouse died, your basis would be $200,000 (50% of $300,000 + 50% of $100,000).