Investment Calculator

How This Investment Calculator Works

This calculator projects how an investment could grow using compound annual growth. Choose a lump sum, a recurring contribution, or both, set an expected annual return, and it compounds that return year over year — showing your future value, total returns, and an inflation-adjusted "real" value, alongside a risk range based on how volatile your portfolio might be.

Lump Sum vs. Recurring Investment (Dollar-Cost Averaging)

A lump sum invested today has the maximum amount of time to compound. Recurring investing — often called dollar-cost averaging (DCA) — spreads contributions out on a schedule, so each dollar gets less time compounding on average, but you're not betting everything on a single day's price.

With this calculator's own defaults — a $50,000 lump sum at a 10% expected return (9.5% after a 0.5% fee) over 15 years — the balance grows to roughly $195,000, about $145,000 in returns on the original $50,000. Investing $500 a month instead over the same 15 years grows to roughly $192,000 — despite contributing $90,000 in total, nearly double the lump sum. That gap is compounding at work: the lump sum's money has been growing the whole time, while later DCA contributions haven't had as long to compound.

Why the Calculator Shows a Range, Not Just One Number

Markets don't return the same percentage every year — actual results swing above and below the average. The "Volatility" input approximates that swing, and the Best Case / Worst Case figures apply it around your expected value so you can see a plausible range instead of a single overconfident number. A higher stock allocation raises this volatility estimate; more bonds and cash lower it.

Why a Small Fee Makes a Big Difference

The Management Fee input is subtracted directly from your expected return before it compounds, and fees compound in reverse — every dollar paid in fees is a dollar that no longer earns future returns. Over a multi-decade horizon, the difference between a 0.5% and a 1.5% annual fee can be tens of thousands of dollars, even though the yearly difference looks small.

Nominal Value vs. Real (Inflation-Adjusted) Value

The headline "Future Value" is in nominal, future dollars. The "Inflation-Adjusted Value" converts that back into today's purchasing power using your inflation rate assumption — at 3% inflation, prices roughly double every 24 years, so a large future balance can buy less than it looks like it should. "Real Return" reflects growth in actual purchasing power, and will always read lower than the nominal return.

What Asset Allocation Changes (and What It Doesn't)

The stocks/bonds/cash/other split feeds the portfolio risk estimate — it doesn't directly change your expected return, since that's controlled separately by the "Expected Annual Return" field. Use allocation to reflect how aggressive or conservative your actual portfolio is, which in turn should inform a realistic return assumption to enter above.

Why Time Horizon Matters More Than Almost Anything Else

Compounding is exponential, not linear — the same rate of return produces dramatically more growth the longer it runs. Starting a decade earlier, even with smaller contributions, often beats starting later with much larger ones, simply because there are more compounding periods. If you're deciding between investing now or waiting, the calculator's period field makes that trade-off easy to see side by side.