Assumptions
This is a quick reality check, not a full retirement plan. Results are shown in today's dollars and use a simple glide path — one expected return while you're working and another (usually lower) in retirement. It finds the earliest age at which your savings can fund a constant gross income target and still last to your planning age in at least your chosen share of simulated markets.
The retirement phase is run as a Monte Carlo simulation with year-to-year return swings to capture sequence-of-returns risk. Returns are nominal compound (geometric) averages; accumulation compounds that expected return, while Monte Carlo converts it to the matching average annual return.
Acknowledgement: Return and volatility assumptions are adopted from PWL Capital.