ESPlanner is able to use Monte Carlo simulation to provide a very powerful statistical analysis to help you understand how risk factors into or changes how we view what is otherwise an average or ideal trajectory of our retirement income and living standard. We can tell the program in the assumptions inputs that we expect to earn an 8.5% return on our retirement investments. But of course the chance of this 8.5% recurring year after year without variation is not likely, to say the least.