How to Use the 401(k) Calculator
The most common retirement planning mistake is treating a 401(k) like a savings account — depositing money and hoping for the best. This calculator turns your numbers into a concrete projection so you can see exactly what your retirement looks like before it arrives.
Enter your current salary, contribution rate, employer match details, current age, and target retirement age. Add your existing balance if you already have one. The calculator handles compounding, salary growth, employer matching, vesting schedules, inflation adjustment, and the Traditional vs. Roth tax comparison — all at once.
Understanding Your Results
The results panel shows six key figures. The Projected Balance is the nominal (face-value) amount you'll have at retirement, alongside the inflation-adjusted real value in today's dollars. The gap between those two numbers often surprises people — at 3% inflation over 30 years, the real value is about 41% of the nominal figure.
Estimated Monthly Income applies the 4% safe withdrawal rule — the rate at which researchers at Trinity University found a portfolio would last at least 30 years in most historical market scenarios. It's a starting point, not a guarantee.
The breakdown bar shows how much of your final balance comes from your own contributions, employer match, and investment growth. In most long-horizon projections, investment growth is the dominant force — which is exactly why time in the market matters so much.
What Is a 401(k)?
A 401(k) is an employer-sponsored retirement savings plan governed by Section 401(k) of the Internal Revenue Code. It was created by Congress in 1978 and grew rapidly after benefits consultant Ted Benna recognized its practical potential in 1980. Today, over 70 million Americans participate in 401(k) plans holding more than $7 trillion in assets, according to the Investment Company Institute.
The defining feature is tax deferral. In a Traditional 401(k), your contributions reduce your taxable income today — you pay income tax only when you withdraw funds in retirement. In a Roth 401(k), you contribute after-tax dollars, but all withdrawals in retirement are completely tax-free. Both variants shelter your investment growth from annual taxation, which dramatically accelerates compounding over decades.
Why the Employer Match Is Your Highest-Return Investment
No legal investment delivers a guaranteed 50–100% instant return. Yet that's precisely what an employer match is. If your employer matches 50% of contributions up to 6% of salary, contributing that 6% gives you an immediate 50% return before a single dollar is invested. Not capturing this match is the equivalent of declining a pay raise.
A 25-year-old earning $60,000 who captures a 50% match on 6% of salary will accumulate an additional $187,000 in match contributions alone by age 65 — assuming 7% annual growth and 2% annual raises. That figure does not count the growth on their own contributions. The earlier you start, the more that match compounds.
The Formula Behind the Projection
The calculator builds the projection year by year using the future value of a growing annuity formula. Each year, it adds your contributions (which grow with your salary), your employer match (subject to the vesting schedule), and applies investment returns to the entire balance.
Where FV is future value, PV is the present (starting) balance, r is the annual growth rate, n is years, and PMT is the annual contribution (yours plus the vested employer match). Since salary — and therefore contributions — grow over time, the calculator iterates year by year rather than applying a single closed-form calculation.
Traditional vs. Roth: A Tax Comparison That Matters
The choice between Traditional and Roth 401(k) is fundamentally a bet on your future tax rate. The math is straightforward: if your tax rate is higher now than it will be at withdrawal, Traditional wins. If your tax rate is lower now than at withdrawal, Roth wins.
The complication is that nobody knows future tax rates with certainty. Congress has changed them repeatedly. Many retirees find their effective tax rate is lower in retirement because they no longer have earned income, mortgage interest deductions have ended, and their spending needs are lower. A common strategy is to diversify: contribute to Traditional during high-earning years and Roth during lower-income years or early career.
2025 IRS Contribution Limits
The IRS adjusts 401(k) limits annually for inflation. For 2025, the employee contribution limit is $23,500. Employees aged 50 and older can add a standard catch-up contribution of $7,500, for a total of $31,000. Under the SECURE 2.0 Act, a new super catch-up provision applies to workers aged 60–63: they can contribute an additional $11,250, bringing their 2025 maximum to $34,750. Total contributions from all sources (employee + employer) cannot exceed $70,000 in 2025.
The calculator monitors your inputs against these limits and displays a warning if your projected annual contribution exceeds the applicable IRS cap. It does not automatically cap contributions — that's a decision you should make with your plan administrator.
The Real Cost of Starting Late
Marcus starts contributing $500 per month to his 401(k) at age 25, earning 7% annually, and stops at age 35 — contributing for exactly 10 years. Sarah starts at 35 and contributes $500 per month all the way to age 65 — contributing for 30 years. At 65, Marcus has more. He contributed $60,000 over 10 years; Sarah contributed $180,000 over 30 years. The compound growth on Marcus's early decade simply cannot be overcome by three decades of later contributions.
This is the core argument for starting early. Even small contributions in your 20s grow into significant wealth by retirement. Waiting until you "can afford it" costs more than the contributions themselves — it costs the compounding those contributions would have earned.
Vesting Schedules and Job Changes
Vesting determines which employer contributions are legally yours if you leave before full vesting. Under a 3-year cliff vesting schedule, leaving after two years means forfeiting 100% of employer match. Leaving after year three means keeping all of it. Graded schedules are more forgiving — a 5-year graded schedule typically gives you 20% ownership per year, so leaving after 3 years keeps 60% of accumulated employer match. This calculator lets you select your vesting schedule to include the correct match figures in projections.
How Inflation Changes Your Outlook
A projected balance of $1.2 million in 35 years sounds substantial. In today's purchasing power at 3% annual inflation, that's roughly $427,000 in real terms. The calculator shows both figures so you plan in terms of what your money will actually buy, not just the nominal dollar amount. Most financial planners recommend targeting a balance equivalent to 10–12 times your final salary in real (inflation-adjusted) terms.
Important Disclaimer
This calculator is for educational and planning purposes only. Investment returns are not guaranteed, tax laws change, and individual circumstances vary significantly. The 4% withdrawal rule is a historical guideline, not a contractual promise. Always consult a licensed financial advisor or Certified Financial Planner (CFP) before making retirement contribution decisions.