Investment Calculator

Calculate your investment return and watch wealth compound

The investment return calculator shows how any lump sum or regular contribution strategy grows over time, using compound interest with an annual return rate you specify. Enter your starting amount, monthly contributions, expected annual return, time horizon, and (optionally) an inflation rate — and get your total future value, ROI, CAGR, and real (inflation-adjusted) return instantly. A year-by-year table and growth chart let you see exactly when the compounding curve starts to accelerate. Everything runs locally in your browser — no account, no upload.

The math uses the standard compound interest formula with monthly contribution: FV = P × (1+r)^n + PMT × ((1+r)^n − 1) / r, where P is the starting principal, r is the monthly rate (annual rate ÷ 12), n is the number of months, and PMT is the monthly contribution. The calculator then derives ROI ((FV − total invested) / total invested), CAGR ((FV/P)^(1/years) − 1), and inflation-adjusted real value (FV / (1+inflation)^years).

The power of compound interest — why time matters more than amount

Albert Einstein reportedly called compound interest the eighth wonder of the world. Whether or not he said it, the math is genuinely remarkable. At a 7% annual return, money doubles roughly every 10 years (the Rule of 72: 72 ÷ 7 ≈ 10). A 25-year-old investing $10,000 and leaving it alone until 65 ends up with $149,000 — without adding a single dollar. A 35-year-old making the same $10,000 investment only ends up with $76,000 by 65. Those 10 extra years of compounding are worth $73,000 by themselves — more than seven times the initial investment.

This is why the first rule of long-term investing is to start as early as possible, even with small amounts. Regular contributions amplify the effect: adding $200 per month to that $10,000 at 7% for 40 years (age 25 to 65) grows to $590,000, of which $106,000 is the original principal plus contributions and $484,000 is pure compound growth. The calculator makes this visible by breaking down each year's ending balance into: original lump sum, cumulative contributions, and cumulative interest earned.

Choosing a realistic expected return for your projection

The expected return you enter is the most consequential variable in the calculation — and the one with the most uncertainty. For broadly diversified stock market index funds (S&P 500, total world), historical real returns (after inflation) have been approximately 5–7% per year over 20+ year periods. Nominal returns (before inflation) average around 7–10%. Bonds have historically returned 2–4% real. Real estate (REITs) typically 5–7% real. High-yield savings accounts currently offer 4–5% nominal but this fluctuates with the Fed rate.

For conservative planning, use 5–6% (real, inflation-adjusted). For moderate planning, use 7%. For aggressive (full equity, long horizon), use 9–10% nominal. The calculator lets you toggle between nominal and real return inputs and shows both the nominal future value and the inflation-adjusted value side by side. Running the same inputs at a few different return assumptions — say 5%, 7%, and 9% — gives you a realistic range rather than false precision on a single number.

Investment calculator comparison — Bankrate, NerdWallet, SmartAsset

Bankrate's investment calculator is the most widely used online tool and handles lump sum plus monthly contributions well, but has no CAGR output, no inflation adjustment, and no year-by-year breakdown table. NerdWallet's calculator shows future value nicely but lacks inflation and CAGR. SmartAsset's investment calculator includes inflation adjustment but the interface is cluttered and it requires choosing a state (oriented toward US tax planning). The Calculator Site's investment calculator is comprehensive but looks dated and lacks a visual chart. Investor.gov's compound interest calculator (SEC-backed) is trustworthy but bare-bones.

This calculator combines the most useful outputs of all of them: future value, total contributions vs. interest breakdown, ROI, CAGR, inflation-adjusted real value, year-by-year table, and a growth chart — in one interface that runs entirely in your browser. No account required, no state-specific assumptions, and the math is shown transparently so you can verify it. For investors who want to understand the compounding math rather than just trust a black box, this is the right tool.

Practical scenarios — retirement, down payment, college fund

For retirement planning: enter your current savings, monthly contribution (or use the 15% of income rule of thumb), expected return (6–7% real is typical for a diversified portfolio), and years until retirement. The result shows your projected nest egg in both nominal and real (today's purchasing power) terms. Divide the real result by 25 to estimate the annual income it can safely support (the 4% withdrawal rule). For a house down payment: enter your current savings, monthly savings amount, a conservative return (4–5% for a high-yield savings account or short-term bonds since you'll need the money soon), and your target timeline in years.

For a college fund: 529 plans invested in age-based index funds typically earn 6–8% annually over an 18-year horizon. Enter your initial contribution, monthly addition, and 18-year time frame to project the balance at college age. For financial independence / FIRE: model your current savings and savings rate, target a 25× annual expenses balance (which supports a 4% safe withdrawal rate indefinitely based on historical data), and find the year the two lines cross. These are all scenarios where having a fast, no-sign-up, browser-based calculator is more practical than setting up a spreadsheet or using a platform that requires an account.

The mathematics of investment returns: CAGR, the Rule of 72, and why geometric mean matters

CAGR (Compound Annual Growth Rate) is the single most important number for evaluating any investment. It answers the question: if the investment grew at a perfectly smooth annual rate, what would that rate be? The formula is CAGR = (End Value / Start Value)^(1/n) − 1, where n is the number of years. A $10,000 investment that reaches $27,000 after 10 years has a CAGR of ($27,000/$10,000)^(1/10) − 1 = 10.43% per year. This is more informative than saying the investment "went up 170%" because it lets you compare across different time horizons and benchmark against indices. The S&P 500's CAGR from 1926 to 2024 is approximately 10.3% nominal — though individual decades ranged from as low as −0.9% (the 2000s, including two crashes) to as high as 18% (the 1990s).

The Rule of 72 is a mental shortcut for estimating how long it takes money to double. Divide 72 by the annual return percentage: at 7%, money doubles every 72 ÷ 7 ≈ 10.3 years; at 10%, every 7.2 years; at 12%, every 6 years. This rule is accurate to within a fraction of a percent for rates between 6% and 12%, and it makes compounding timelines instantly tangible. A 30-year-old who earns 7% real returns on their portfolio will see their money double roughly at 40, 50, and 60 — three doublings, turning $50,000 into $400,000 in real purchasing power before they retire.

A critical and widely misunderstood concept is the difference between the arithmetic mean return and the geometric mean return (CAGR). Suppose a stock rises 50% one year and falls 50% the next. The arithmetic mean is (50% + (−50%)) / 2 = 0% — it looks like you broke even. But you did not: $100 grew to $150, then fell to $75. The geometric mean (CAGR) is ($75/$100)^(1/2) − 1 = −13.4% per year. This gap, called variance drag, grows larger the more volatile the investment. It means two portfolios with identical arithmetic average returns will produce different wealth outcomes if one is more volatile. Always use CAGR — not average annual return — to compare investment performance.

Dollar-cost averaging vs. lump-sum investing: what the research actually shows

Dollar-cost averaging (DCA) means investing a fixed amount at regular intervals — say, $500 every month — regardless of whether the market is up or down. Because the amount is fixed, DCA automatically buys more shares when prices are low and fewer when prices are high, producing a lower average cost per share than the average share price over the same period. This is often presented as a strategy to beat the market, but that framing is misleading. DCA's primary benefit is not return maximisation — it is risk reduction and behavioral consistency. It removes the temptation to time the market and prevents the devastating mistake of investing everything right before a peak.

The honest research picture is more nuanced than DCA advocates often admit. Vanguard's 2012 study examined lump-sum investing versus 12-month DCA across the US, UK, and Australian markets over rolling 10-year periods. Lump-sum investing outperformed DCA approximately two-thirds of the time, by an average of about 2.3% over the deployment period. The logic is simple: markets rise more often than they fall, so cash waiting on the sidelines is a drag on returns. If you have a windfall — an inheritance, a bonus, proceeds from selling a house — the statistically optimal move is to invest it immediately.

However, the study also found that DCA was the better choice emotionally for investors who would otherwise hold cash indefinitely out of fear, or who would panic-sell a lump-sum position during the first dip. A strategy you can stick with beats an optimal strategy you abandon. There is also an important distinction between deliberate DCA and natural DCA: investing your paycheck every two weeks as it arrives is technically dollar-cost averaging, and it is optimal — you are investing immediately with each paycheck. The DCA debate applies specifically to the decision of what to do with a windfall. The monthly contribution field in this calculator models both use cases: ongoing DCA from income, or a planned deployment of a lump sum over time.

Asset class historical returns: stocks, bonds, real estate, gold, and crypto

Understanding what different asset classes have actually returned over long periods is essential for setting realistic inputs in any investment calculator. US large-cap stocks (S&P 500) have returned approximately 10.3% nominal CAGR from 1926 to 2024, or roughly 7–7.5% real after inflation. US small-cap stocks have historically returned around 11.9% nominal — the small-cap premium was formally documented by Rolf Banz in 1981 and has persisted in most subsequent decades, though it has been weaker since 2000. International developed-market stocks (MSCI EAFE) have returned approximately 7–8% nominal CAGR since the index's inception in 1970, with significant decade-to-decade variance and a prolonged underperformance relative to the US since 2010. The diversification argument for international exposure rests on mean reversion and correlation reduction, not recent returns.

US long-term Treasury bonds have returned approximately 5–6% nominal historically, but that figure is dominated by the extraordinary 1982–2020 bull market in bonds as interest rates fell from 15% to near zero. Over the 2022 rate-hiking cycle, long-term Treasuries lost roughly 30% of their value — the worst bond bear market in over a century — demonstrating that bonds carry real risk at extended durations. Gold has returned approximately 7.5% nominal CAGR since 1971 when Nixon ended the Bretton Woods gold standard, but with extreme volatility, no income, and multi-decade drawdown periods (gold fell roughly 70% in real terms from 1980 to 2000). Real estate investment trusts (REITs) have returned approximately 11–12% nominal CAGR since the FTSE NAREIT index began in 1972, combining rental income yield and appreciation — making them one of the strongest-returning asset classes historically.

Cryptocurrency poses a fundamental challenge for historical CAGR analysis. Bitcoin's CAGR since 2013 is extraordinarily high in nominal terms, but several compounding factors make this figure unreliable as a forward estimate: the asset class is only 15 years old (far too short a history to infer a long-run expected return), survivorship bias is severe — the vast majority of cryptocurrency projects launched since 2013 have gone to zero or near zero, and Bitcoin itself has experienced multiple drawdowns exceeding 80%. Any CAGR figure for crypto reflects a single historical episode, not a structural return premium with a causal mechanism like the equity risk premium or the income yield of real assets. For projection purposes, most financial planners recommend treating cryptocurrency as a speculative satellite position rather than assigning it a CAGR in a long-term model.