This is a glossary of terms related to this calculator, personal finance, and retirement.

If you think a term is missing from here that should be added, please contact me.

4% Rule

The 4% Rule is a rule of thumb that says you can safely withdraw 4% of your portfolio each year of your retirement. After the first year, this value is adjusted for inflation for each subsequent year of your retirement.

The 4% Rule was originally described by William Bengen, and it was later popularized by the Trinity Study.


A way to validate a retirement plan by seeing how it performed using historical data. FI Calc is a backtesting calculator. For more, read the guide on backtesting.


A community of individuals who follow John Bogle's philosophy of investing. The Variable Percentage Withdrawal (VPW) strategy was created by members of the Bogleheads community.


A popular retirement calculator that also uses a backtesting strategy. It was created by a member of the FIRE community named Bo. cFIREsim was created after FIRECalc.


Another popular retirement calculator that uses a backtesting strategy.


Inflation is the tendency of a currency to purchase less as time goes on. Inflation from year to year is generally modest (around 3%), but it can add up to have a considerable effect over long periods of time, such as retirements. For this reason, it is important to understand and factor in inflation when planning for retirement.

John Bogle

The founder of Vanguard. John Bogle is known for creating the first index fund, as well as for popularizing the idea of mutual funds. Read more on his Wikipedia page.

The Trinity Study

The Trinity Study is a colloquial name given to a study that was published by three professors at Trinity College which helped to popularize the 4% Rule. Employing a backtesting strategy similar to Bengen's, they arrived to the same conclusion.

The name of the paper is "Retirement Savings: Choosing a Withdrawal Rate That Is Sustainable" and the authors are Philip L. Cooley, Carl M. Hubbard, and Daniel T. Walz.


An investment company that is popular among retirees for its selection of low-cost index funds. It was created by John Bogle.

William Bengen

A financial advisor who first proposed the 4% Rule of retirement planning through a backtesting analysis. His original paper, "Determining Withdrawal Rates Using Historical Data," was published in 1994.