Variable Percentage Withdrawal

Variable Percentage Withdrawal (VPW) is a dynamic strategy developed by the Bogleheads community. It combines actuarial calculations with a dynamic planning horizon, recalculating your withdrawal amount annually based on your age, current portfolio balance, and asset allocation.

The annual withdrawal percentage is calculated using the Excel PMT formula:

Where:

• is the expected portfolio return (the discount rate).
• is your remaining life expectancy from the IRS Uniform Lifetime Table (Publication 590-B).
• is the present value (-1, representing your current portfolio balance).
• is the future value (0, as the portfolio is designed to deplete by the end of your lifespan).
• represents payments due at the beginning of the period (1).

For example, a 65-year-old retiree with a 35-year remaining horizon ($n=35$) and a expected return of 3.76% on a 60/40 portfolio will calculate a dynamic percentage, which is then applied directly to the balance. You can run these models using engines like FICalc.

The Terminal-Horizon Vulnerability Because the PMT formula assumes a hard landing ($\mathit{FV}=0$), the withdrawal percentage rises dramatically as you age. At $n=10$ and a 4% expected return, the formula calls for an 11.5% withdrawal; at $n=5$ it demands over 21%. If a severe sequence-of-returns shock hits when you are 88, a 20% drop in the market translates to an immediate 20% drop in your nominal spending at a life stage where you have zero flexibility. VPW must be paired with a guaranteed income floor (Social Security, a QLAC, or a private annuity) to cover baseline expenses, using the VPW stream strictly for discretionary spending.