The famous Trinity Study established that a 4% initial withdrawal rate, adjusted annually for inflation, historically resulted in portfolio survival over a 30-year period. However, early retirees (FIRE) often face retirement horizons of 40 to 50 years, requiring more conservative SWR mathematics.
To ensure your capital lasts indefinitely, many experts recommend lowering your SWR to 3.25% or 3.5%. At these rates, the probability of portfolio depletion drops to near zero, even in worst-case historical scenarios like the Great Depression or 1970s stagflation.
Additionally, introducing dynamic spending rules—where you reduce withdrawals slightly during market downturns—dramatically increases portfolio resilience. Model these variables regularly in your planning dashboard to find the perfect balance between savings targets and security.