When one joint tenant dies, one-half of the JTWROS assets receives a stepped-up basis.
Let's say that Grandma's stock had a value of $100,000 at her death. Since the stock was in a JTWROS account, each of your parents-in-law owned 1/2 of the shares. Each half would have a stepped-up basis of $50,000. When one parent-in-law dies, their half of the shares would be stepped-up to its value as of the date of death. The surviving partner's half would retain its original $50,000 basis.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
