FIRE Prowess is easy to calculate. It’s simply the change in your net worth, divided by your gross income, for any time period.
FIRE Prowess = Change In Net Worth / Gross Income
Most of us will have FIRE Prowess scores between 0.0x and 1.0x. The higher your FIRE Prowess number is, the better you are doing at increasing your net worth.
Numbers above 1.0x mean your net worth is growing faster than your income, which is an incredible result, presumably driven by both a relatively frugal lifestyle in the context of your income, and strong investment results.
A negative number means your net worth is headed in the wrong direction, which could be caused by spending more than you earn, a job loss, borrowing money to purchase depreciating assets, poor investment performance, or many other factors.