About Investment Modeler

What Is Investment Modeler?

Investment Modeler is a free, straightforward tool for understanding how compound interest grows your investments over time. It's designed for one purpose: help you visualize scenarios and plan your financial future without complexity or sales pitches.

We built this because existing investment calculators are either cluttered with ads, locked behind paywalls, or so overly complex that they confuse rather than clarify.

How Investment Modeler Works

Our Methodology

Investment Modeler uses the standard compound interest formula taught in finance courses and verified by Khan Academy and the U.S. Securities and Exchange Commission:

A = P(1 + r)^n + PMT × [((1 + r)^n - 1) / r]

Where:

• A = Future value (what you'll have)
• P = Principal (your starting amount)
• r = Annual return rate (as a decimal)
• n = Number of years
• PMT = Regular monthly contribution

This formula is:

• Mathematically correct
• Widely accepted in financial planning
• Based on decades of academic research
• Transparent (you can verify it anywhere)

Inflation Adjustment

We use the standard inflation-adjusted return calculation:

Real Return = ((1 + Nominal Return) / (1 + Inflation Rate)) - 1

This shows your purchasing power growth, not just raw numbers.

What Investment Modeler Does NOT Do

This tool does not:

• Predict the future (markets fluctuate; actual returns vary)
• Account for taxes (tax impact depends on account type and your bracket)
• Include fees or expense ratios (real portfolios incur costs)
• Guarantee results (past performance ≠ future results)
• Provide personalized investment advice (consult a financial advisor)
• Track your actual investments (calculations happen in your browser; we store nothing)

Why these limitations matter: This calculator shows average scenarios, not real-world complexity. Taxes, fees, and market volatility are real. Use this tool to understand compound interest; use a financial advisor for personalized planning.

Your Privacy

We take privacy seriously:

• Zero data collection: All calculations happen in your browser. Your numbers never leave your computer.
• No tracking: We don't use cookies, pixels, or analytics to track your behavior.
• No selling: We never store, sell, or share your information.

This calculator is designed for your use alone. You can close it, refresh, or clear your browser—your data is never stored on our servers.

Sourcing & Trust

Our methodology is sourced from:

• Khan Academy — Compound interest formulas and education
• U.S. Securities and Exchange Commission (SEC) — Investment disclosure standards and risk guidance
• Federal Reserve — Historical inflation data and economic methodology
• Yahoo Finance and FRED — S&P 500, FTSE 100, and MSCI World prices plus CPI-U and 10-year Treasury yields used on the historical performance page for backtests, crash flags, and DCA vs lump sum
• FTSE 100 & MSCI World indices — International market data

All of these are public, government, or academic sources you can verify yourself.

Disclaimers

You assume all investment risk. Securities and investments are subject to market risk, including the potential loss of principal. Past performance does not guarantee future results. Actual returns vary based on market conditions, inflation, taxes, fees, and countless other factors.

Consult a professional: Before making investment decisions, speak with a certified financial planner (CFP), registered investment advisor (RIA), or qualified tax professional who understands your personal situation.

Market volatility is real: This calculator shows average returns. Real markets fluctuate. A 7% average return might include years with -20% and +30% swings. Make sure you can tolerate that volatility before investing.

Not investment advice: Nothing on this site constitutes a recommendation to buy, sell, or hold any security. This is educational content only.

Limitations to Know

1. Fixed Returns Assumption

Real markets are volatile. This calculator assumes consistent returns; actual markets vary.

2. No Tax Modeling

Tax impact depends on account type (401k, IRA, brokerage, etc.), your tax bracket, and holding periods.

3. No Inflation Modeling for Asset Types

Different assets (stocks, bonds, real estate) respond differently to inflation. This tool treats all investments the same.

4. No Sequence-of-Returns Risk

This calculator assumes you don't withdraw money. Real retirement involves withdrawals, which means sequence of returns (when you retire relative to market conditions) matters enormously.

5. No Fee Modeling

Real portfolios have expense ratios (0.03%–2% annually). This calculator doesn't account for them.

Questions?

If you have questions about:

• How compound interest works: See our compound interest guide
• Historical returns: See S&P 500 history and backtests
• Real-world scenarios: See investment scenarios
• Technical questions: See our FAQ

For investment advice specific to your situation, consult a financial professional.

Contact

If you've found Investment Modeler helpful, or have feedback, we're committed to keeping this tool free, simple, and accurate.

Investment Modeler — Understanding compound growth, simply.

Last updated: September 2026

Disclaimer: Investment Modeler is an educational tool. It is not investment advice. Securities involve risk, including potential loss of principal. Past performance does not guarantee future results. Consult a qualified financial advisor before making investment decisions.