401(k) Growth Calculator

How Does a 401(k) Grow?

A 401(k) can grow from three primary sources: money already in the account, new contributions, and investment returns. Employer contributions can add another source of money when a plan provides a match or other employer contribution.

Investment gains can then earn additional returns over time. This compounding effect becomes more significant as the investment period grows, although actual market returns fluctuate and can be negative.

What Is Compound Growth in a 401(k)?

Compound growth means investment returns can be earned not only on the money contributed to the account, but also on previous investment gains.

For example, if a balance earns a positive return one year, the next year's return is calculated on a larger balance—assuming the gains remain invested. Over long periods, this can make investment growth an increasingly large part of the projected account value.

Actual 401(k) investments do not earn a fixed return every year. This calculator uses an average annual return assumption to create an understandable projection.

How Much of a 401(k) Balance Comes From Investment Growth?

There is no universal percentage. The answer depends on your starting balance, years invested, contribution amount, employer contributions, investment return, fees, and withdrawals.

The calculator separates your projected ending balance into:
starting balance + employee contributions + employer contributions + investment growth
so you can see how much each source contributes to the result.

What Return Should I Use for a 401(k) Growth Calculator?

There is no single return assumption that is appropriate for every 401(k). Actual returns depend on the investments held, market performance, asset allocation, fees and the period being measured.

Rather than treating one rate as a forecast, use the calculator to test multiple assumptions. For example, compare a lower, middle and higher hypothetical return and see how sensitive the final result is to each. Do not treat any example rate on this page as a prediction or investment recommendation.

Do 401(k) Fees Affect Compound Growth?

Yes. Fees and expenses can reduce investment returns and therefore reduce the amount remaining in the account to compound.

Different plans and investments can charge different expenses, including investment expenses and certain administrative fees. Check your plan's disclosures and investment documents to understand the fees that actually apply to your account.

Why Show a 401(k) Balance in Today's Dollars?

A future balance can look much larger simply because prices may also be higher in the future. The Today's Dollars view discounts the projected balance using the inflation assumption entered in the calculator.

This gives an approximate way to compare the future balance with today's purchasing power. It is still only an estimate because future inflation cannot be known in advance.

How Does an Employer Match Affect 401(k) Growth?

Employer matching contributions add more money to the account, subject to the plan's matching formula, eligibility rules and vesting provisions. That money may then participate in future investment gains or losses along with the rest of the invested balance.

If you are unsure how your employer's formula works, use the 401(k) Employer Match Calculator before entering the match assumptions here.

Does This Calculator Use the 2026 401(k) Contribution Limits?

For the 2026 projection year, the calculator recognizes applicable current limits:

• Employee elective-deferral limit: $24,500
• Standard eligible age-50+ catch-up: $8,000
• Higher catch-up for eligible participants ages 60–63: $11,250
• Defined-contribution annual-additions limit (IRC § 415(c)): $72,000
• Annual compensation limit (IRC § 401(a)(17)): $360,000

Important: Future IRS limits beyond 2026 are not yet known and must not be presented as facts. If the calculator models contributions increasing in later years, those increases are projection assumptions—not official future IRS contribution limits.

See the full 2026 401(k) Contribution Limits guide →

How Are Future Contribution Limits Handled?

The calculator applies known 2026 limits to the current projection year where relevant. For future years, official statutory limits are unknown. Therefore the calculator does not fabricate future IRS limits.

If future contributions are modeled as increasing with salary or by a user-entered growth rate, those values are clearly labeled as hypothetical contribution assumptions—never as official IRS forecasts.

How We Calculate Your 401(k) Growth

The calculator projects the account period by period. At a high level:

The ending balance then becomes the next period's beginning balance. Where salary-based contributions are used, employee and employer contribution amounts can change as modeled salary changes.

Inflation does not reduce the nominal account balance. It is used separately to calculate the optional Today's Dollars result. Actual market returns vary from year to year. A constant return assumption is used only to make scenario comparisons understandable.

Sources & Methodology

Current 2026 statutory limits are verified against:

• Internal Revenue Service — Notice 2025-67 and current retirement-plan limit guidance
• U.S. Securities and Exchange Commission / Investor.gov — Mutual Fund Fees and Expenses
• U.S. Department of Labor Employee Benefits Security Administration (EBSA) — Understanding Your Retirement Plan Fees

Last verified: October 2026.