How Utilix financial tools work — data sources, model assumptions, editorial review standards, and what every calculator does and does not account for.
Updated May 2026 · Reviewed against current market data
Every Utilix financial calculator is a planning and education tool, not investment advice. The models are grounded in peer-reviewed academic research and long-run historical market data. They are designed to help you reason about order-of-magnitude numbers, not to predict the future.
All calculations run locally in your browser — nothing is sent to a server. Your inputs persist in the URL so you can bookmark and share your plan.
All FIRE tools default to a 7% real (inflation-adjusted) annual return, based on the long-run historical average of the US S&P 500 with dividends reinvested (source [2]). Because it is already real, every projected dollar represents today's purchasing power — no separate inflation adjustment is needed.
The 4% safe withdrawal rate originates from the 1994 research by William Bengen (source [3]) and the 1998 Trinity Study (source [1]). It means a retiree can withdraw 4% of a diversified stock/bond portfolio in year one, then inflation-adjust that dollar amount each year, with a historically high probability of not running out of money over a 30-year retirement. This implies a FIRE number of 25× annual expenses.
Bengen (1994) tested a 50/50 large-cap stocks / intermediate-term US Treasuries mix. The Trinity Study (Cooley, Hubbard & Walz, 1998) tested S&P 500 stocks with long-term corporate bonds at 0/100, 25/75, 50/50, 75/25 and 100/0 ratios. The popular “60/40” label is a later simplification and is not a portfolio used in either foundational paper.
For longer retirement horizons (40+ years, typical for early retirees), many planners prefer 3.25–3.5% (Pfau, 2011 — source [4]; Kitces, 2012 — source [5]). The Retirement Withdrawal Calculator lets you model any SWR directly.
Accumulation calculators (FIRE, Coast FIRE, FIRE Progress, Lean vs Fat FIRE) compound monthly — the portfolio grows at r/12 each month while contributions are added. The Coast FIRE present-value discounting uses annual compounding.
Taxes are not modelled across any tool. All inputs and outputs are treated as post-tax figures. If you save in tax-advantaged accounts (401(k), IRA, ISA, NPS), the effective drag is substantially lower than in a taxable brokerage account — but you should validate your final FIRE number against your personal tax situation or consult a qualified financial advisor.
All FIRE calculator pages are reviewed annually against current market data and academic consensus. Each page displays an “Updated [Month Year]” freshness signal at the top. If assumptions or default values change — for example, if the academic consensus around safe withdrawal rates shifts — the affected calculators and this page are updated and re-dated.
The current defaults (7% real return, 4% SWR) reflect the consensus as of May 2026. They are reasonable for a US equity-weighted portfolio with a 30-year horizon. Early retirees with 40+ year horizons should consider 3.25–3.5% SWR.