How we get the numbers
Here is how we work out each number on the main page. All of it comes from real data.
Where the data comes from
Fund prices and dividends: Yahoo Finance data for the SPDR S&P 500 ETF (SPY), every trading day from January 29, 1993 to September 30, 2026.
Company dividends: Yahoo Finance data for The Coca-Cola Company (KO), checked against the company's own news releases.
Retirement account limits: IRS.gov.
We name these funds and companies only to show where real numbers come from. This is not a recommendation.
Try your own start
Each month, your amount buys shares at the closing price on the first trading day of the month.
Each dividend buys more shares at the closing price on its cutoff date (also called the ex-dividend date).
Parts of a share count too.
The value at the end is the number of shares on September 30, 2026, times the price that day.
The fund's own yearly fee is already inside its price. Taxes, trading costs and inflation are not taken out.
We check the end value a second way, with the price that already counts dividends. For the January 2010 start, the two agree within 0.1%.
The biggest drop
We look at the price with dividends counted, from your first buy to September 30, 2026.
The biggest drop is the largest fall from a high point to the low point after it.
For the January 2010 start, it was about 34%, from February 19, 2020 to March 23, 2020.
For starts up to September 2007, it was about 55%, from October 9, 2007 to March 9, 2009.
The second start
The second start is always 5 years after yours. If that is after September 2025, it is 5 years before yours.
That way, one lucky date can't tell the whole story.
Low, middle and high
We use the month-end price with dividends counted.
For 10 years, we look at every 10-year stretch from January 1993 to September 2026. There are 285 of them. For 20 years, we look at every 20-year stretch.
For each stretch, we find the steady yearly growth that turns the start price into the end price.
Low is the worst stretch. High is the best stretch.
Middle is the compounded yearly rate over the whole time, January 1993 to September 2026: 10.81% a year. It is one even rate that gives the same end value. Real years went up and down. It is not one stretch, and it is not an average.
To look ahead, we start from your real value on September 30, 2026. We add your amount at the start of each month and grow it at each of the three rates.
Every projection has this label: Projection based on past averages. Past results don't guarantee future results.
Nothing runs longer than 20 years.
Dividends
In 2025, the company paid 51 cents a share four times: $2.04 a share for the year.
So 10 shares got $5.10 each time, or $20.40 for 2025, before taxes.
Readability
We test our words with the Flesch-Kincaid grade. We aim for about a 6th-grade reading level.