How this calculator works
Prices come from Yahoo Finance monthly adjusted closes (splits and, where Yahoo provides them, dividends). A lump sum buys at the first available month in your chosen year. “Spread that year” splits the dollars across that year’s months. “Every year since” repeats the same dollar amount at the start of each following year.
If a company listed after your start year, the buy happens at the first month of data. Bitcoin uses the BTC-USD ticker. This ignores taxes, fees, and the fact that you might have sold. Past returns are not a forecast.