Methodology
Last updated: May 2026
How assumptions become retirement estimates.
No financial advice
This page explains a model for estimate work. Results are educational and should not be interpreted as personalized financial guidance.
This is an educational planning model. It is designed to compare scenarios clearly, not to predict a single guaranteed date.
What the model calculates
The calculator uses your current savings, monthly contributions, target retirement age, inflation, return assumptions, withdrawal rate, and optional Social Security bridge as inputs.
The FIRE number is the nominal target implied by spending needs and withdrawal assumptions, while projected portfolio shows the modeled growth path.
Monte Carlo and volatility
In addition to a deterministic projection, the model runs randomized return sequences based on return and volatility assumptions.
The success rate is the share of simulated outcomes that meet the target. It is a probability estimate, not a guarantee.
What is simplified
The model can omit taxes, fee schedules, employer plan details, exact tax location, pensions, market regime shifts, healthcare and debt details.
For personal decisions, compare your own constraints and consult a qualified professional.
Interpretation and safety notes
Use the result trio together: FIRE number, projected portfolio, and success rate. Any single value on its own can mislead.
No result is a promise. This is a planning aid for estimating ranges.