The calculator
First-year spending$40,000
Spending after the run$222,8682 cuts, 14 raises
Ending portfolio$115,426Horizon completed
Success rate53%1000 seeded paths
10th percentile ending$0
Median ending$83,330
90th percentile ending$3,174,969
How the rails trip
Each year spending is indexed with inflation, then a seeded batch of paths estimates remaining success at the current spend. Below the floor, cut. Above the ceiling, raise. That is the probability-of-success guardrail Kitces described, which only a tool that can actually compute remaining odds can implement. Guyton-Klinger, by contrast, looks only at the current withdrawal rate — see the guardrails explainer.
Assumptions
The displayed path uses the mean return you typed, one year at a time. Remaining success is estimated with 80 seeded paths per review so the page stays usable. The 1,000-path band below is the overall constant-spend check, not the rail estimator.