A mega backdoor Roth is an advanced strategy that allows you to contribute significantly more to a Roth account than the standard annual limits. This works if your 401(k) plan allows after-tax contributions (beyond the normal pre-tax or Roth contributions) and either in-plan Roth conversions or in-service withdrawals.

Here's how it works: After maxing out your regular 401(k) contributions ($23,500 in 2025), you make additional after-tax contributions up to the total annual limit ($70,000 including all contributions), then immediately convert those after-tax dollars to Roth, either within the plan or by rolling to a Roth IRA. The result: a massive amount of money that will grow and be withdrawn completely tax-free in retirement. This strategy requires a specific plan design—not all employers offer it—and significant cash flow to take full advantage. If you're a high earner with extra savings capacity and access to this option, the mega backdoor Roth can dramatically accelerate your path to tax-free retirement wealth.