Using the 401k or Roth 401k CalculatorUse this Roth 401k vs 401k calculator to help determine the option that could work for you and how it might affect your paycheck. Enter your own information into our 401k or Roth 401k calculator. You can easily change the inputs to see what the impact will be. Areas highlighted in red will need to be filled in in order for the 401k calculator to produce meaningful results. You can also generate a report showing how contributions, earnings and taxes will affect the value of both traditional and Roth 401k accounts using your personalized inputs. This analysis can help guide you to answer the question: Which is best option for me – Traditional 401k or Roth 401k?