A Blackout Period is a temporary time during which participants in a retirement plan cannot make changes to their investments, transfer funds, or take distributions. This usually happens when the plan is undergoing a major change—like switching recordkeepers, updating systems, or reorganizing investment options. The blackout period ensures all necessary updates can be made accurately and securely, but it also means participants won’t be able to access or change their accounts until it ends. Employers are generally required to give advance notice if a blackout period will last more than a few days.