A simple tool for calculating compound interest, including 401(k), is available at the website of the U.S. Securities and Exchange Commission. The tool works by calculating interest based on five values: current principal, monthly addition, years to grow, interest rate and the compound frequency per year.
Clicking Calculate returns the result of the calculation. The user can clear the table by clicking the Reset button. The SEC also offers more detailed explanations for each of the five values. Users can reveal these explanations by hovering their mouse cursors over the question marks to the right of each of the value lines.