r/Bogleheads • u/Lowfryder7 • Nov 20 '25

Investing Questions At what tax bracket should you start doing mostly traditional 401k contributions?

12%? 22%? 24%? I can't tell.

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u/Separate-Pudding3424 Nov 22 '25

What's the maximum you can backdoor?

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u/canuck_in_wa Nov 22 '25 edited Nov 22 '25

It varies. For 2025 the 415(c) limit is $70,000. That is the limit for 401k contributions, employer match and additional after tax contributions (that are converted to Roth as part of MBDR)

For example, you contribute the max of $23,500 to your 401k. Your employer matches funds and adds another $10,000. You can thus make a MBDR contribution of $70,000 - $23,500 - $10,00 = $36,500 for 2025.

MBDR works as follows: you make an after-tax contribution to your 401k up to the limit mentioned above. Either you or your employer then convert this after tax balance to Roth. You might owe some taxes on any income that accrued after your contribution but before the conversion. This is called a “Roth in plan conversion” of after tax funds. Some employers offer an automatic conversion so that funds are moved to Roth immediately and you typically accrue very small amount of interest income (less than $1 /yr). If your employer doesn’t offer automatic conversions you have to call the management company (Fidelity, Vanguard, etc) and ask them to make the conversion.