What does consistent investing
actually build over a lifetime?
Adjust the inputs below to model long-term wealth growth across four investment strategies. Use the calculator tabs to adjust assumptions, compare taxes, and see what timing and income illustrations may mean for the result.
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This calculator shows how money grows when invested consistently over time. It is not a prediction — it is an illustration of how different rates of return and time horizons produce dramatically different outcomes. Use it to understand the mechanics of long-term investing, not as a substitute for personalized financial advice.
Already have money invested? Enter it here. This amount will compound at the same rate as your ongoing contributions over the full period. The calculator assumes this balance is already held in the same account type you are modeling.
This is how much you invest each month — through a 401(k), IRA, or brokerage account. Contribution limit indicators will appear if your amount exceeds IRS annual limits. The Assumptions tab can model annual contribution increases; the Overview reflects those settings when enabled.
Starting age is when you begin investing. Retirement age is when you stop contributing and the portfolio is valued. The gap between these two numbers — not the monthly amount — is the single most powerful variable in this calculator.
S&P 500 — tracks 500 of America's largest companies. Broad diversification, historically reliable long-term growth. Available in nearly every 401(k) and IRA. Nasdaq-100 / QQQ — a familiar growth-oriented, technology-heavy benchmark. It has outperformed the S&P 500 in many historical periods, but with higher concentration, greater volatility, and severe drawdowns, including the dot-com crash. Growth 80/20 Portfolio — a growth-oriented static mix of 80% stocks and 20% bonds. It is more aggressive than a traditional balanced portfolio, but easier to understand and audit than a custom target-date glide path. Custom Rate — enter any return assumption you want to test.
By default, dollar amounts are shown in nominal future dollars — meaning the actual dollar amounts you'd see in your account decades from now, before adjusting for inflation. If Inflation-Adjusted mode is enabled in the Assumptions tab, the Overview will also show values in today's dollars — meaning the calculator translates future dollars into today's purchasing power, so a $1M figure in 40 years isn't compared apples-to-oranges with $1M today. $1M in 40 years is not the same as $1M today, so use the Assumptions tab to toggle between nominal and inflation-adjusted views.
The Taxes tab models a simplified Roth vs. pre-tax comparison, including capital gains tax on reinvested paycheck savings. The Timing & Income tab shows the cost of waiting and a simple 4% rule illustration.
A simple priority order for most investors: (1) Contribute enough to your 401(k) to capture the full employer match — this is an immediate 50–100% return on that money. (2) Max your Roth IRA ($7,500/year in 2026) — tax-free growth for decades. (3) Return to your 401(k) up to the $24,500 annual limit. (4) Any remaining savings go into a taxable brokerage.
A caveat worth taking seriously: not every dollar belongs in a retirement account. Money locked in a 401(k) or IRA is generally inaccessible without penalty until age 59½. Keeping a meaningful portion of your savings in liquid, taxable accounts — for emergencies, a home down payment, a business opportunity, or simply optionality — is a feature, not a flaw. This calculator focuses on long-term growth, not account-by-account allocation. Use the Taxes tab to compare Roth vs. pre-tax outcomes.
NOTE — All projections assume that dividends and distributions are reinvested rather than taken as cash (in an actual brokerage account, this may require a dividend reinvestment election or manual reinvestment). The return assumptions used here are nominal — meaning they reflect actual future dollar growth before adjusting for inflation. When Inflation-Adjusted mode is enabled in the Assumptions tab, projected balances are translated into today's purchasing power using the selected inflation rate. S&P 500: ~10.5% avg (1957–2025). Nasdaq-100 / QQQ: ~12% illustrative growth assumption. Growth 80/20 Portfolio: growth-oriented static mix of 80% stocks and 20% bonds (stocks ~10.5%, bonds ~4.5%, blended ~9.3%). Inflation and annual contribution growth controls live in the Assumptions tab and are reflected across the calculator when enabled. Not financial advice.
Assumptions
Set the assumptions that drive the calculator: compounding, inflation, and annual contribution increases
Taxes
A simplified Roth vs. pre-tax comparison, including reinvested paycheck tax savings.
Net take-home after all taxes · same contribution · same strategy
Pre-tax contributions reduce taxable income at this rate today
Traditional withdrawals taxed as ordinary income
Applied to gains in the taxable account holding reinvested paycheck savings
Timing & Income
See what waiting may cost, estimate the contribution needed to reach a target, and use the 4% rule to translate a projected portfolio balance into rough annual income.
What does waiting to start actually cost you at retirement?
Want a specific balance by retirement? Estimate the starting monthly contribution required to get there.
A simple income illustration based on the ending portfolio values above — not a full withdrawal plan.
Why use it here? This calculator uses 4% only as a teaching shortcut — a way to make the projected balance easier to understand as possible annual income. It does not mean the portfolio is guaranteed to last forever, and it does not mean each strategy shown is equally appropriate for retirement withdrawals. The 4% rule is most commonly discussed with diversified stock/bond portfolios; a more concentrated or aggressive portfolio may carry greater sequence-of-returns risk once withdrawals begin.
Methodology
What the calculator is, what it is not, and the assumptions behind the numbers.
A long-term investment growth illustration. It shows how starting balance, monthly contributions, time, return assumptions, inflation, taxes, and contribution increases can affect projected portfolio values.
It is not a retirement-readiness calculator, withdrawal plan, tax plan, investment recommendation, or individualized financial advice. It does not estimate spending needs, Social Security, pensions, healthcare costs, or whether you are on track to retire.
This calculator uses the S&P 500 and Nasdaq-100 / QQQ as familiar reference points. The S&P 500 is a broad large-cap U.S. stock benchmark, while the Nasdaq-100 is more concentrated and more heavily weighted toward technology and growth companies. QQQ is included in the label because it is one of the most widely recognized ETFs associated with Nasdaq-100-style exposure.
The 12% figure is an illustrative growth assumption, not a forecast. It is meant to sit between different historical reference points: QQQ's ETF history began in 1999 near the dot-com bubble, while the Nasdaq-100 Index has a longer history and has outperformed the S&P 500 in many periods. Future returns could be lower than past periods, especially because many of the largest Nasdaq-100 companies are already among the largest businesses in the world.
This calculator uses the 4% rule only as an illustration. It does not mean the portfolio is guaranteed to last forever, and it does not mean every strategy shown is equally appropriate for retirement withdrawals. The rule is most commonly discussed in connection with diversified stock/bond portfolios, and actual withdrawals depend on taxes, market returns, inflation, timing, spending behavior, and account type.