Deterministic vs Monte Carlo, percentile bands, risk of ruin, and the readiness score.
The value of a plan change is best seen by comparing two scenarios side by side — net worth, success probability, and percentile bands
A backtest replays your plan through real historical return sequences — "what if I'd retired in 1929, 1966, or 2000?"
Monte Carlo runs your plan through thousands of randomized scenarios
Your decisions move the plan as much as the markets do — saving a raise, holding through a downturn, and choosing a drawdown approach all change the outcome
The 10th percentile is your "bad-luck floor" — 90% of simulated futures end up better than this point
A healthy plan has an emergency fund, a sustainable withdrawal rate, manageable debt, no single oversized position, and a solid savings rate
Real markets have interrelated factors — stocks, bonds, rates, inflation, housing
Deterministic forecasts assume constant returns; Monte Carlo samples from distributions
Percentile bands show the range of outcomes across Monte Carlo trials
The Horizons Retirement Readiness score is 0–100, combining five components
Success rate is the fraction of trials where the plan works