Roth 401(k) Calculator: Project Tax-Free Retirement Growth
Project how a Roth 401(k) could grow when funded with after-tax pay, so that qualified withdrawals in retirement are entirely tax-free.
Adjust the inputs and select Calculate for a full breakdown.
Year-by-year growth schedule
Compare Common Scenarios
How the numbers shift across typical situations for this calculator:
| Scenario | Future value | Total contributions | Total interest earned |
|---|---|---|---|
| $25k · $700/mo · 7% · 30yr | $1,056,892.13 | $277,000.00 | $779,892.13 |
| $0 · $500/mo · 8% · 35yr | $1,146,941.24 | $210,000.00 | $936,941.24 |
| $120k · $1k/mo · 6% · 20yr | $859,265.43 | $360,000.00 | $499,265.43 |
| $60k · $900/mo · 7% · 25yr | $1,072,589.62 | $330,000.00 | $742,589.62 |
How This Calculator Works
Enter the current Roth 401(k) balance, the average annual return you expect, the years until retirement, and your monthly contribution. The calculator compounds the balance monthly and adds each contribution, showing the projected balance and the growth.
The Formula
Future Value with Regular Contributions
P = starting amount, PMT = monthly contribution, r = monthly rate (annual ÷ 12), n = number of months
Worked Example
With $25,000 saved, $700 added monthly, and a 7% average return over 30 years, a Roth 401(k) reaches about $1,056,900. Contributions account for $277,000; the rest is tax-free investment growth.
Key Insight
A Roth 401(k) combines a high contribution limit with tax-free qualified withdrawals. One wrinkle: an employer match is usually placed in a pre-tax account, so part of the total may still be taxed in retirement.
Roth vs traditional — the tax bracket question
Mathematical equivalence: in a world with identical tax rates today and at retirement, Roth and Traditional 401(k) produce IDENTICAL after-tax results. Both provide tax-free growth on contribution amount. The difference is when tax is paid (now vs at retirement).
Roth advantage: pay tax NOW at known rate; never tax again. Best when: current marginal rate < expected retirement rate; want tax diversification; expect substantial Social Security and required distributions in retirement (avoiding income stacking).
Traditional advantage: deduct contribution NOW; pay tax in retirement. Best when: current marginal rate > expected retirement rate; want maximum current tax savings; expect lower-spending retirement.
Most workers should use SOME Roth: tax diversification provides flexibility in retirement income strategy. Even 'traditional is mathematically optimal' workers benefit from 20-50% Roth allocation to manage Social Security taxation and Medicare premiums in retirement.
Strategic Roth allocation by career stage
Early career (22-30) — typically low income, low tax bracket (12-22%). Roth heavily favored: pay 12-22% tax now to avoid potentially 24-32% tax at retirement. Aggressive Roth allocation appropriate.
Mid career (30-45) — peak earnings, peak tax bracket (24-32% for most). Mathematical close call. Many advisors recommend 50-70% Roth allocation for tax diversification.
Late career (45-55) — close to retirement, can model retirement income more precisely. Traditional often wins for high earners expecting lower retirement spending. But Roth has unique advantages: no RMDs at age 73; tax-free legacy to heirs.
Near retirement (55-65) — focus on Roth conversion strategies. After leaving employment, gap years between retirement and Social Security/RMDs provide low-income years ideal for Roth conversions. Convert traditional balances to Roth at low marginal rates; pay tax now to escape future RMD requirements.
Roth vs Traditional 401(k) — illustrative scenarios
Reference scenarios for $20K annual contribution over 30 years at 7% return.
| Scenario | Roth final after-tax | Traditional final after-tax | Winner |
|---|---|---|---|
| 22% bracket now, 22% retirement | $1.42M | $1.42M | Tie |
| 22% bracket now, 32% retirement | $1.42M | $1.24M | Roth +$180K |
| 32% bracket now, 22% retirement | $1.42M | $1.42M (pre-tax $1.82M − tax) | Tie at sim. rates |
| 32% bracket now, 32% retirement | $1.42M | $1.42M | Tie |
| Today vs Tax-Free Future (Roth) | $1.82M tax-free at retirement | $1.82M pre-tax, taxed at withdrawal | Roth wins if rates rise |
Calculation assumes contributions in Roth use $20K of after-tax dollars (requires earning $25K-$28K pre-tax in 22-32% brackets). Traditional contributions use $20K pre-tax. Equivalent comparison: $25K pre-tax to Traditional vs $20K post-tax to Roth produces nearly identical math when tax rates stay constant. Differences emerge when tax rates change between now and retirement.
Frequently Asked Questions
How is a Roth 401(k) taxed?
Contributions are made with after-tax pay, and qualified withdrawals — including all growth — are tax-free once the account is five years old and you are 59½ or older.
How does it differ from a traditional 401(k)?
A traditional 401(k) is funded pre-tax and taxed on withdrawal; a Roth 401(k) is funded after-tax and withdrawn tax-free. The Roth wins if your retirement tax rate is similar or higher.
Is the employer match also tax-free?
Usually not. Employer matching contributions typically go into a pre-tax account, so that portion and its growth are taxed as income when withdrawn.
How does a Roth 401(k) compare with a Roth IRA?
Both offer tax-free qualified withdrawals, but a Roth 401(k) has a much higher contribution limit and no income cap, while a Roth IRA offers wider investment choice.
Is there a contribution limit?
Yes. The IRS sets an annual 401(k) contribution limit, with a higher cap for savers age 50 and older. Keep contributions within that limit.
When is this calculator unreliable?
As a 'Roth always wins' or 'Traditional always wins' guide — the optimal choice depends on relative tax brackets today vs in retirement, both uncertain. For honest analysis, model scenarios with retirement bracket lower than current, equal, and higher. Make decision based on which scenarios seem most likely AND degree of regret minimization. Most workers benefit from some Roth allocation for tax diversification regardless of mathematical optimum.
References & Authoritative Sources
- Internal Revenue Service (IRS) — Designated Roth Account Information · consulted June 1, 2026 · Federal regulator on Roth 401(k) rules
- U.S. Department of Labor — EBSA — Roth 401(k) Plan Information · consulted June 1, 2026 · Federal employee benefits regulator
- Vanguard — Roth vs Traditional Analysis — Roth IRA vs Traditional IRA Considerations · consulted June 1, 2026 · Industry research on Roth vs Traditional decision
Related Calculators
Data Sources & Benchmarks
This calculator draws on 3 independent, dated sources. The starting values for expected annual return are taken from the benchmarks below and refresh whenever the snapshots are updated.
Methodology & Review
Roth 401(k) growth uses compound interest formula with regular contributions. The calculator returns balance projection. Roth 401(k) contributions are post-tax (no tax deduction); growth is tax-free; qualified withdrawals (age 59½+, account 5+ years old) are tax-free. 2024 contribution limit same as traditional 401(k): $23,000 + $7,500 catch-up if 50+. Employer match goes into traditional (pre-tax) account, not Roth (becomes taxable in retirement). RELIABILITY: Reliable for documented contribution and return assumptions. Less reliable as forward projection because the 'Roth vs traditional' decision depends critically on future tax bracket vs current tax bracket — uncertain assumption. For young workers in lower current bracket, Roth typically beats traditional; for high-bracket workers expecting lower retirement bracket, traditional often wins.
Updated