401(k) Calculator
Calculate 401(k) growth with employer matching, contribution limits, and investment return projections to plan your retirement savings.
Calculator
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Projects 401(k) balance at retirement with employer match and compound monthly growth. Employer match = Match% x min(employee contribution, Match Limit% of contribution). 2024 contribution limit: $23,000 ($30,500 if 50+).
Last reviewed: January 2026
Worked Examples
Example 1: Age 30 to 65
Background & Theory
The 401k Calculator applies the following established principles and formulas. Finance and investing rest on the foundational concept of the time value of money: a dollar received today is worth more than a dollar received in the future, because present funds can be deployed to earn a return. This principle underlies virtually every valuation technique in modern finance. The future value of a present sum P growing at rate r over n periods is expressed as FV = P(1 + r)^n, while the present value of a future cash flow FV is PV = FV / (1 + r)^n. Compound growth amplifies returns significantly over long horizons, a dynamic often described as the eighth wonder of the world. Net Present Value (NPV) extends these mechanics to evaluate investment projects by summing the present values of all expected cash flows minus the initial outlay: NPV = sum[CF_t / (1 + r)^t] - C_0. A positive NPV indicates the project creates value above the required return. The Internal Rate of Return (IRR) is the discount rate that sets NPV to zero, providing a single percentage benchmark for project comparison. The risk-return tradeoff is the central tension of investment theory. Higher expected returns generally require accepting greater uncertainty. Harry Markowitz formalized this in Modern Portfolio Theory by demonstrating that portfolio variance can be reduced through diversification when assets are imperfectly correlated. The efficient frontier represents the set of portfolios offering the maximum return for a given level of risk. The Capital Asset Pricing Model (CAPM) extends this by introducing the market portfolio as a reference, defining expected return as E(r) = r_f + beta * (E(r_m) - r_f), where beta measures an asset's sensitivity to systematic market risk. Asset classes — equities, fixed income, real assets, and alternatives — differ in their return profiles, liquidity, and correlations. Strategic asset allocation determines long-run target weights based on investor objectives and risk tolerance, while tactical allocation permits short-run deviations to exploit perceived mispricings. Discount rates used in valuation models must reflect the cost of capital appropriate to the risk of the cash flows being discounted, a point stressed in corporate finance texts from Brealey, Myers, and Allen through to Damodaran.
History
The history behind the 401k Calculator traces back through the following developments. The formal practice of lending at interest dates to ancient Mesopotamia, where the Code of Hammurabi around 1750 BCE regulated interest rates on grain and silver loans. Banking as an institutional activity took root in medieval Italy, with merchant bankers in Florence and Venice financing trade across Europe through instruments such as bills of exchange. The Medici family operated one of the most sophisticated banking networks of the fifteenth century, pioneering double-entry bookkeeping and correspondent banking relationships. Organized equity markets emerged in the early seventeenth century. The Dutch East India Company (VOC), chartered in 1602, issued shares to the public and created the Amsterdam Stock Exchange — widely regarded as the world's first formal stock exchange. The VOC allowed investors to buy and sell shares freely, establishing the template for the joint-stock company. The period also produced the Dutch tulip mania of 1636 to 1637, one of history's first recorded speculative bubbles, in which tulip bulb futures contracts reached extraordinary prices before collapsing. England's financial revolution followed in the late seventeenth century with the founding of the Bank of England in 1694 and the development of government bond markets. The South Sea Bubble of 1720 illustrated the dangers of speculative excess and contributed to early securities regulation. Throughout the eighteenth and nineteenth centuries, industrialization created enormous demand for capital, fueling the expansion of stock exchanges in London, Paris, New York, and beyond. The New York Stock Exchange, formalized in 1817, became the world's dominant equities market by the twentieth century. The Great Crash of 1929 and subsequent Great Depression prompted the US Securities Act of 1933 and Securities Exchange Act of 1934, establishing the SEC and mandatory disclosure requirements. Harry Markowitz published his landmark portfolio selection paper in 1952, launching quantitative finance. The CAPM emerged in the 1960s through work by Sharpe, Lintner, and Mossin. John Bogle launched the first retail index fund in 1976, democratizing diversified investing and challenging active management orthodoxy.
Frequently Asked Questions
Formula
FV = PV(1+r/12)^n + (PMT + Match)(1+r/12)^n-1)/(r/12)
Projects 401(k) balance at retirement with employer match and compound monthly growth. Employer match = Match% x min(employee contribution, Match Limit% of contribution). 2024 contribution limit: $23,000 ($30,500 if 50+).
Frequently Asked Questions
What is the difference between simple and compound interest?
Simple interest is calculated only on the original principal: SI = P × r × t. Compound interest is calculated on the growing balance — each period's interest is added to the principal before the next period is calculated. The formula is A = P(1 + r/n)^(nt), where n is compounding frequency. On a $10,000 investment at 8% over 20 years, simple interest yields $26,000 while annual compounding yields $46,610 — a 79% difference. More frequent compounding (monthly vs. annually) further accelerates growth, which is why high-yield savings accounts advertise APY (annual percentage yield) rather than the nominal rate.
What is the Rule of 72?
The Rule of 72 is a quick way to estimate how long it takes to double your money. Divide 72 by your annual interest rate to get the approximate number of years. At 8% annual returns, your investment doubles in about 9 years.
How does inflation affect investment returns?
Inflation silently erodes purchasing power even when your nominal balance grows. If your portfolio earns 8% annually but inflation runs at 3%, your real return is approximately 4.85% (calculated as (1.08 ÷ 1.03) − 1), not simply 5%. Over 30 years, $100,000 at 8% nominal grows to $1,006,266, but in today's purchasing power it is worth only $413,000 in a 3% inflation environment. This is why bonds yielding 4-5% in a 4% inflation period offer almost no real growth. Equities have historically returned 6-7% above inflation over long periods, making them essential for preserving real wealth.
What is dollar-cost averaging?
Dollar-cost averaging (DCA) means committing a fixed dollar amount — say $500 per month — into an investment on a set schedule, regardless of whether markets are up or down. When prices fall, your fixed amount automatically buys more shares; when prices rise, it buys fewer. This lowers your average cost per share over time versus trying to time the market. DCA also removes emotion from the decision, preventing panic selling or over-buying at peaks. Studies show most individual investors who try to time the market underperform a simple DCA strategy, largely due to behavioral biases. It is especially effective for volatile assets like equities or index funds.
What is the difference between a traditional and Roth retirement account?
Traditional 401(k) and IRA contributions reduce your taxable income today — a $6,500 contribution in the 22% bracket saves $1,430 in taxes immediately — but all withdrawals in retirement are taxed as ordinary income. Roth accounts accept after-tax contributions with no upfront deduction, but qualified withdrawals (age 59½+, account held 5+ years) are completely tax-free, including all growth. If you expect to be in a higher tax bracket in retirement than today, Roth wins. If you expect lower rates in retirement, traditional wins. Many advisors suggest holding both types to give yourself tax flexibility when withdrawing. Roth IRAs also have no required minimum distributions (RMDs), unlike traditional accounts.
What is asset allocation and why does it matter?
Asset allocation is how you divide a portfolio among stocks, bonds, cash, real estate, and other asset classes. Research by Brinson, Hood, and Beebower found that over 90% of a portfolio's long-term return variability is explained by asset allocation, not individual security selection or market timing. A common starting rule is to hold (110 minus your age)% in equities and the rest in bonds — so a 35-year-old would hold 75% stocks. As you approach retirement, shifting toward bonds and cash reduces volatility but also expected returns. Rebalancing annually back to target weights systematically forces you to sell high and buy low.
Reviewed by Sahil, Senior Finance & Tax Editor · Editorial policy