If you have access to both Roth and Traditional retirement accounts (through a 401(k), an IRA, or both), the question 'which should I use?' comes up every contribution cycle. Most online answers default to 'always Roth when you're young.' That's a reasonable rule of thumb, but it's worth understanding the actual decision logic underneath it.

The core comparison

The question that drives the decision is how today's tax rate compares to the expected tax rate in retirement.

• Higher expected tax rate in retirement than today: Roth contributions tend to be the more efficient choice, since tax is paid at the lower rate now and withdrawals come out tax-free later.
• Lower expected tax rate in retirement than today: Traditional contributions tend to be more efficient, since the deduction comes at the higher current rate and withdrawals are taxed at the lower rate later.
• Uncertain about future tax rates: a roughly 50/50 split between Roth and Traditional is one common way to hedge.

Who often leans toward Roth

• Younger workers in lower tax brackets early in their careers, who expect significant income growth.
• People who expect substantial assets in retirement (pensions, large 401(k)s, paid-off rental properties) that may push them into higher brackets later.
• Anyone who values flexibility and predictability in retirement (Roth withdrawals don't add to taxable income).

Who often leans toward Traditional

• Higher earners in their peak income years, especially those who expect to retire to a lower-tax state.
• People nearing retirement who expect to be in a lower bracket once they stop working.
• Anyone trying to manage their current Adjusted Gross Income for things like ACA health insurance subsidies or other income-based programs.

A compound growth calculator can model both scenarios with different tax assumptions.

Sources

• IRS, Roth IRAs: https://www.irs.gov/retirement-plans/roth-iras
• IRS Publication 590-B, Distributions from Individual Retirement Arrangements (IRAs): https://www.irs.gov/publications/p590b
• HealthCare.gov, Modified Adjusted Gross Income (MAGI): https://www.healthcare.gov/glossary/modified-adjusted-gross-income-magi/