What does consistent investing
actually build over a lifetime?
Set a monthly amount, set your ages, and see what consistency builds. The tabs go deeper: assumptions, taxes, and what waiting actually costs.
Principles
for long-term wealth
I built this to show what consistent investing does over time. None of it is a prediction. Returns never arrive in a straight line, and nobody can tell you what the next forty years look like. What I can show you is the mechanics: how time, rate of return, and consistency interact, and why starting early matters more than almost anything else you control.
Already have money invested? Enter it here and it compounds right alongside your contributions. I assume it sits in the same account type you're modeling.
How much you invest each month, whether through a 401(k), IRA, or brokerage account. A warning appears if you exceed an IRS annual limit. The Assumptions tab can layer in annual increases from raises.
Starting age is when you begin. Retirement age is when the portfolio gets valued. The distance between those two numbers does more work than any other input here, including the monthly amount.
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 — 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 you're looking at nominal future dollars, the actual balance you'd see in your account decades from now. Flip on Inflation-Adjusted mode in the Assumptions tab to translate everything into today's purchasing power. A million dollars in forty years buys a lot less than a million today. The toggle keeps you honest about that.
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.
Where I'd put dollars first, for most people: capture your full 401(k) employer match before anything else. Matched dollars are an instant 50 to 100% return, and nothing else on this page competes with that. Then max a Roth IRA ($7,500 in 2026) for decades of tax-free growth. Then go back to the 401(k) up to the $24,500 limit, and put whatever remains in a taxable brokerage.
One caveat I take seriously: not every dollar belongs in a retirement account. Money in a 401(k) or IRA is generally locked up until age 59½. Keeping real savings liquid for emergencies, a down payment, or a business opportunity is worth the tax cost of a brokerage account. This calculator models growth, not account allocation. The Taxes tab compares Roth and 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: ~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 compounding illustration. It shows how starting balance, monthly contributions, time, returns, inflation, and taxes interact to produce an outcome.
Advice. It doesn't know your spending, your Social Security, your health costs, or whether you're on track to retire. It answers one question well: what does consistent investing build over time?
The S&P 500 is the obvious broad-market benchmark. For the growth slot, the textbook choice would be the Russell 1000 Growth index, but almost nobody outside the industry knows it. The Nasdaq-100 measures largely the same thing, and it's the index you actually recognize, and ETFs that track it (such as Invesco's QQQ) are available in nearly every brokerage. For a teaching tool, I'd rather use the benchmark you'll encounter in real life than the academically pure one you won't.
I anchored 12% to the index's actual record, then chose below the average. The Nasdaq-100 has returned about 14.25% per year since its 1985 inception and roughly 13% per year over the last 20 years. The worst realistic starting point in its history, buying the oldest ETF tracking the index (Invesco QQQ) the month it launched in March 1999, near the top of the dot-com bubble, still produced about 11% per year with dividends reinvested. So 12% sits under every multi-decade average and above only that single worst entry point. Two warnings belong next to it: the index fell 83% from 2000 to 2002 and needed most of two decades to fully recover, and most professional forecasts, Vanguard's among them, expect US growth stocks to return less over the next decade than they did over the last four.
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.