Investment Calculator

Final portfolio value (what the calculator outputs)

Principal — your initial lump-sum deposit

Periodic contribution — your monthly addition to the portfolio

Annual interest rate as a decimal (e.g., 7% → 0.07)

Compounding periods per year (12 for monthly, 365 for daily)

Investment time horizon in years

Total Capital Invested

The sum of your initial deposit plus all monthly contributions: P + (PMT × 12 × t). This is what you put in, net of any returns.

Final Value (A)

The output of the compound interest formula — the projected portfolio value at the end of your selected horizon, before taxes.

Total Return (Interest)

Final Value minus Total Contributed. This is the purely interest-generated wealth — what compounding added above and beyond your savings.

ROI on Contributions

(Interest Earned ÷ Total Contributed) × 100. Tells you what percentage return you earned on the money you actually deposited.

Effective Annualized Yield

(FV ÷ Total Contributed)^(1/t) − 1. A simplified CAGR-like metric showing the equivalent annual return over the whole period. Not identical to IRR.

Interest Share of FV

What percentage of the final portfolio balance is pure interest growth vs capital you deposited. The higher this is, the more compounding has worked for you.

🕐 Time in Market Beats Timing

Starting 10 years earlier can double your final portfolio with the same contribution rate. A 25-year-old investing $300/month at 7% until 65 will have $792K. Starting at 35 produces only $380K — less than half, despite contributing for 30 fewer years.

📈 Dollar-Cost Averaging (DCA)

Investing a fixed amount monthly regardless of market conditions reduces the average purchase price over time. This calculator models DCA precisely via the PMT term — keeping contributions constant regardless of rate swings.

🔄 Reinvest Dividends

If your investment generates dividends, reinvesting them (rather than withdrawing) dramatically amplifies compounding. Even a 2% dividend yield reinvested adds roughly 25–35% to your 20-year total at 5% base growth.

💰 Maximize Tax-Advantaged Accounts

In the US, 401(k) and IRA contributions grow tax-deferred (or tax-free for Roth). The effective APR of a Roth IRA at 7% outperforms a taxable account at 7% with 22% tax drag by the equivalent of 1.5–2% APR annually.

⚖️ Rebalance Annually

A portfolio drifting to 80% equities from a target 60/40 carries more risk than intended. Annual rebalancing sells outperformers and buys underperformers — maintaining risk level while systematically buying low.

📊 Factor in Inflation

The calculator outputs nominal values. To estimate real purchasing power, subtract ~2–3% expected inflation from your return rate. A 7% nominal return at 3% inflation = ~4% real return. Run scenarios at both rates for an honest range.

💹How accurate is this investment calculator?

The calculator uses the standard compound interest formula with exact periodic compounding — not approximations. It matches values produced by Excel's FV() function. The main sources of divergence from real-world outcomes are: (1) taxes on interest/dividends, (2) investment fees and expense ratios, (3) variable returns (markets don't return exactly 7% every year), and (4) contribution timing (this model assumes end-of-period contributions). For a more conservative estimate, reduce the rate by 0.5–1% to account for fees.

💹What is the difference between ROI and annualized yield in the KPI dashboard?

ROI = (Interest Earned ÷ Total Contributed) × 100 — a simple total return ratio ignoring time. If your $140,000 in contributions grows by $172,000, ROI = 123%. The Effective Annualized Yield is a CAGR-like metric: (FV / Contributed)^(1/t) − 1. It's not identical to IRR (Internal Rate of Return) because it doesn't account for the timing of each contribution. Consider the annualized yield as an approximation — for precise IRR, you would need XIRR in Excel.

💹Should I use monthly or annual compounding in the calculator?

Match the compounding frequency to your actual investment account. High-yield savings accounts (HYSAs) typically compound daily. Index funds and ETFs do not compound in the traditional sense — they provide returns through price appreciation and dividend reinvestment. For a buy-and-hold index fund model, annual compounding is technically most accurate. Monthly compounding overestimates slightly. For comparing accounts, always check the APY (Annual Percentage Yield) — it normalizes different compounding frequencies to a single comparable figure.

💹What does the AI Deep Review do and is it private?

The AI Deep Review sends a compact summary of your inputs (principal, rate, years, compounding, monthly contribution) and outputs (final value, ROI, yield) to our server, which forwards them to a Gemini language model. The model returns a structured analysis: input quality assessment (is your rate realistic? Is your horizon adequate?), result sanity check (does the ROI look reasonable?), and recommended actions. No personal identifying information is sent — only the numerical inputs and outputs visible in the calculator. You can review the model's response and decide whether to act on it.

💹How do I calculate compound interest without a calculator?

For a lump sum with no contributions, use: A = P × (1 + r/n)^(n×t). Example: $10,000 at 7% annually for 20 years = 10,000 × (1.07)^20 = 10,000 × 3.8697 = $38,697. The Rule of 72 provides a quick mental estimate: at 7%, money doubles every ≈10.3 years. For monthly contributions, the calculation requires the annuity formula above and is most easily handled by a calculator like this one or Excel's FV() function.

💹What is a realistic annual return rate to use?

Historical returns for a global equity index (e.g., MSCI World) average 8–10% nominal per year over very long periods. After accounting for inflation (2–3%), real returns average 5–7%. After fund fees (0.05–0.5% for index ETFs, up to 1–2% for actively managed funds), net real returns are typically 4.5–6.5%. Conservative financial planning uses 5–6% nominal; aggressive models use 8–10%. The calculator's default of 7% represents a reasonable midpoint for long-term equity investing — adjust for your specific allocation and risk tolerance.