Glossary · Tax
A wash sale occurs when a security is sold at a loss and a substantially identical security is purchased within thirty days before or after the sale.
The rule applies across all of a taxpayer's accounts, including a spouse's and including retirement accounts — which is why harvesting decisions have to be made with the household in view rather than one account at a time.
This is one of the strongest practical arguments for holding a client's relationship on a single system: a wash sale created by an account the advisor cannot see is still a wash sale.
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