401(k) Growth Calculator
Pure compounding only—starting balance plus annual contributions at your chosen return. Unlike the flagship 401(k) calculator, this tool strips out employer match, IRS caps, and inflation so you can see what time and return do in isolation.
Inputs
How to Use This Growth Calculator
Use this tool when you want to isolate compounding itself without employer match, tax, or retirement-plan rules getting in the way.
- Enter starting balance and annual contribution. These two numbers define the capital already working for you and the fresh money added each year.
- Set years and expected return. Use conservative assumptions if you want a realistic planning range instead of an optimistic headline number.
- Compare starting dollars, contributed dollars, and growth. The calculator separates what you put in from what compounding created.
How to Read the Results
Final Balance
The ending account value after all contributions and growth over the period you selected.
Starting Balance
This reminds you how much of the ending result came from money already saved.
Total Contributions
This is the fresh capital added during the projection period.
Growth (Interest)
When this number becomes larger than contributions, compounding is doing the heavy lifting.
What to Do Next
How We Reviewed This Tool
Tool-Level Methodology
- Built this tool as the pure-compounding baseline so users can isolate time, return, and contribution size without match or tax variables muddying the signal.
- Checked the year-by-year table against the summary result to ensure the displayed growth path reconciles with the final balance.
- Used the same long-term return language found elsewhere on the site so growth-only scenarios stay consistent with broader retirement projections.
Assumption Review
- The calculator intentionally strips out employer match, taxes, and IRS plan rules so it can serve as a neutral compound-growth lens.
- Return rate is constant across the projection window, which is useful for planning but not how markets behave in real life.
- This page is best for scenario comparison rather than realistic sequence-of-returns modeling.
Update Log
- Kept the compounding explanation aligned with the site's flagship projection language.
- Reviewed contribution-frequency and return-rate wording so it targets future-value and compound-interest query variants more directly.
- Updated supporting links so users can jump from pure-growth modeling back into plan-specific tools.
Compound Interest: The 401(k) Miracle
Einstein allegedly called compound interest the “eighth wonder of the world.” In a 401(k), it is the single factor that converts modest monthly contributions into a seven-figure retirement balance — if you start early enough.
The Formula
Future Value = Present Value × (1 + r)n + Contributions × [((1 + r)n − 1) ÷ r]
Where r is annual return, n is years. Our tool uses semi-annual compounding, so mid-year contributions earn half a year of growth on average.
Why Starting Early Matters: The $1,000 Test
$1,000 invested at 7% real return:
- In 10 years becomes $1,967
- In 20 years becomes $3,870
- In 30 years becomes $7,612
- In 40 years becomes $14,974
Every decade roughly doubles your balance — but only if you stay invested. This is the single strongest argument for maxing your 401(k) early in your career, even if it feels tight.
Return Rate Realism
| Asset Class | Real Return | Volatility |
|---|---|---|
| S&P 500 (large-cap US stocks) | ~7.0% | ~18% |
| Small-cap US stocks | ~7.5% | ~22% |
| 10-year Treasury bonds | ~2.0% | ~8% |
| 60/40 stock/bond portfolio | ~5.0% | ~11% |
| Target-date 2050 fund | ~6.0% | ~13% |
Source: Shiller S&P 500 dataset & Ibbotson SBBI. Past performance does not guarantee future results.
Frequently Asked Questions
What is a 401(k) growth calculator?
A 401(k) growth calculator projects how your account balance grows over time through compound interest on both your starting balance and ongoing contributions. It answers 'how much will my 401(k) be worth in X years?' at a given rate of return.
How is compound interest calculated in a 401(k)?
In most 401(k)s, compounding is effectively continuous as dividends and capital appreciation accrue throughout the year. Our calculator uses semi-annual compounding to approximate this — more conservative than annual, more realistic than daily.
What rate of return is realistic for a 401(k)?
Historical S&P 500 real returns (1957–2024) average about 7% after inflation. Diversified stock-heavy portfolios typically use 6–8% real; bond-heavy conservative allocations use 3–5%. Avoid using nominal 10%+ if you care about purchasing power.
Further Reading
- Reviewed by David Jones
- Limits Updated for 2026 IRS contribution caps
- Formulas Verified quarterly
Review & Methodology
- Reviewed by David Jones (calculator methodology).
- Updated for 2026 IRS contribution limits (refreshed after each annual IRS notice).
- Core calculator formulas are re-tested quarterly; limit-driven logic is checked when IRS guidance changes.
- Educational projections only — not investment, tax, or wealth-management advice. Calculations run locally in your browser.