Millions of Americans leave 401(k)s behind when they change jobs, and in many cases, that money ends up in low-return, high-fee "Safe Harbor IRAs" that can erode retirement savings, a new report warns.

By 2030, roughly 13 million former employees are projected to have about $43 billion in retirement assets automatically rolled into Safe Harbors, according to a PensionBee analysis that draws on data from the Employee Benefits Research Institute.

A Safe Harbor IRA is a retirement account your former employer can open to transfer your 401(k) balance, typically if it's under $7,000 and you don't move it within 30 to 60 days after leaving the job.

The accounts are designed to be a safe, temporary home for small balances,........

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