Our calculators use standard time-value-of-money concepts. For compound growth, the base future value formula is:
FV = P ~ (1 + r / n)^(n ~ t)
Where P is principal, r is annual rate, n is compounding frequency, and t is time in years.
For recurring monthly contributions, each contribution is projected forward to the end of the selected period using the same return assumption. Taxes, fees, inflation, and other frictions are excluded unless explicitly stated.