What this example shows
This scenario isolates how the timing of taxation changes the comparison between a Traditional and Roth 401(k) for the peak earner persona. The same pre-tax dollars are contributed either way; the difference comes entirely from when the tax is paid and at what assumed rate.
Because the assumed retirement tax rate is lower here, the Traditional 401(k) comes out ahead under these assumptions.
Assumptions and limitations
The example assumes a constant contribution, a constant annual return, and fixed current and retirement tax rates with no employer match, contribution limits, plan fees, or required minimum distributions.
It is an educational scenario, not tax, legal, investment, or retirement-plan advice. Actual tax rates, brackets, and account rules can change and differ from these assumptions.
How savers use a comparison like this
Use the result as a starting point, then test your own best estimate of your current and future tax rates in the full calculator. The relative direction of the two rates matters more to this comparison than their exact level.
Many savers split contributions between Traditional and Roth accounts specifically because future tax rates are uncertain. This example only models an all-or-nothing choice between the two.