Why Looking at the Past Helps
Seeing how investments grew (or shrank) in the past helps you make smarter money choices. Past results never promise the same in the future, but real history shows you how markets act in good times and bad.
Our calculator uses real market data to show exactly what would have happened if you had put a specific amount of money in on a certain date. These are not guesses. They are real numbers from actual prices and dividends recorded by markets around the world.
Whether you are curious about a stock you almost bought, want to see how long-term investing works, or just want to ask "what if?", our calculator gives you clear, honest answers using real data.
How We Calculate
Where Our Data Comes From
We use three main data sources to make sure numbers are accurate:
- Yahoo Finance (stored locally): Gives us historical prices, dividend events, and stock split info for stocks and ETFs. Prices are adjusted for splits and dividends so every result reflects what a real investor would have seen.
- Coin Metrics: Provides daily price data for major cryptocurrencies (Bitcoin, Ethereum, and others) in USD. Coin Metrics is a trusted, independent crypto data provider used by researchers and money managers worldwide.
- IMF World Economic Outlook and national statistics agencies: Provides inflation data (CPI) for the Inflation Calculator. For the United States, we also cross-check with the Bureau of Labor Statistics (BLS). Data for G20 countries is updated each year.
What Happens if You Pick a Non-Trading Day
When you pick a date, we automatically find the closest day the market was open. Markets are not open every day. Here is how it works:
- Weekends: If you pick a Saturday or Sunday, we use the price from the Friday before, since stock markets are closed on weekends.
- Market Holidays: If the market was closed for a holiday (like Christmas or Thanksgiving in the US), we step back to find the most recent day with real price data.
- Crypto: Crypto markets are open 24/7, so any date is valid. We still check that actual price data exists for the date you pick.
- Data Check: We always confirm that real price data exists for the date we use. We never guess or estimate prices.
What Is Dividend Reinvestment?
Our "Dividend Investor" mode shows what happens when you automatically use dividend payments to buy more shares (sometimes called a DRIP, which stands for Dividend Reinvestment Plan). Instead of taking the cash, you buy more of the same stock:
- Each dividend payment buys more shares at the market price on the day the dividend is paid
- Those extra shares earn their own dividends later on
- This creates a "snowball effect" where the number of shares you own keeps growing over time without putting in extra money
- We calculate the exact number of shares bought with each dividend, including fractional shares, just like real investment apps do
How Precise Are the Calculations?
All calculations avoid rounding errors by using high-precision math. Results are accurate to the cent. Shares are rounded to six decimal places and money amounts to two decimal places, just like a real investment account.
Last reviewed by Nora Kim, March 29, 2026
Market Analysis Reviewer
Important Note
For Learning Only: This calculator is a learning tool to help you understand how investments have performed in the past. It is not financial advice and does not tell you what to buy or sell.
Past Results: Past gains do not guarantee future results. Markets go up and down. All investments carry risk, including losing the money you put in.
What Is Not Included: Our calculations do not account for taxes, trading fees, broker costs, or inflation. Real returns would be lower once you factor those in.
Talk to an Expert: Before making any investment decisions, speak with a qualified financial advisor who knows your personal situation and goals.
Frequently asked questions
Common questions about what this calculator does and does not include.
Is this calculator financial advice?
No. It is an educational tool for historical scenario analysis and does not provide personalized investment advice.
Why can my broker statement differ from these results?
Broker statements may reflect intraday fills, fees, taxes, and account-specific events that are outside this educational model.
How are dividends handled?
Dividend treatment depends on the selected mode and available instrument data, with assumptions documented in the methodology section.
Can I compare purchasing power after inflation?
Yes. Use the inflation calculator as a next step to translate nominal returns into real purchasing power context.