This calculator generates simulation runs for each year of data in our historical dataset (1928 - 2016) based on what you enter above. It is useful for comparing portfolio allocation outcomes, realistic withdraw rates, and setting a savings goal. It outputs the percent of time the simulated nest egg stayed above water or ran out of money.
Some insights into the results this tool unearths:
How the simulations work:
This calculator is NOT a Monte-Carlo simulator in that it does not generate any fake or random data. Instead, this calculator uses historical data and backtests against it. Essentially it replays what happened in each of the years in the dataset given the inputs and then summarizes of the results.
For a 30 year retirement period, this calculator will run a simulation from 1928 to 1958, then it will run a simulation from 1929 to 1959, then from 1930 to 1960, and so on. In simulations that go beyond 2016, it will wrap back to 1928 and count up from there. In this sense, the effect of the great depression is factored in for early and late starting years.
Each individual simulation computes returns by stepping through the years (eg 1928, 1929, ... 1958) and performs the following each year:
Regarding the Annual Withdraw Percent:
The famous Trinity Study suggests a 3-4% withdraw rate is a good place to be: "If history is any guide for the future, then withdrawal rates of 3% and 4% are extremely unlikely to exhaust any portfolio of stocks and bonds...". Keep in mind, this calculator and the Trinity Study rely on backtesting, which means historical data is analyzed for a 'best fit'. Yesterday's best fit may turn out to be a very poor fit in the future. Nobody really knows for sure what will happen next. In general terms, a lower withdraw rate means the nest egg with last longer.
Notes on Inflation:
The numbers this calculator outputs are not inflation adjusted, they are nominal values. The numbers don't translate to actual purchasing power in the starting year of the simulation. However, this calculator does adjust the withdraw amount by the CPI each year of the simulation. For example, given a 30 year retirement and an initial withdraw amount of $50,000, the simulation starting in 1975 would increase the withdraw amount all the way to $181,440 in 2005 (in the final year of that simulation run) based on the change in CPI.
Historical Data Used:
The data this calculator uses can be found at http://people.stern.nyu.edu/adamodar/New_Home_Page/data.html.
Again, this calculator does backtesting. Past performance does not guarantee nor indicate future results.
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