Editorial Process

How we research, fact-check, and maintain the calculators and articles on this site.

Operating principles

Primary sources before opinions

Numbers come from primary sources — IRS revenue procedures (HSA, 401(k), IRA limits), SSA tables (Social Security thresholds), peer-reviewed papers (Trinity Study, Pfau, Bengen), and Mr. Money Mustache for the canonical savings-rate-to-years-of-FIRE table. We name the source whenever a number appears.

One source of truth per fact

Contribution limits, current-year references, and post metadata live in single TypeScript data files (data/contribution-limits.ts, data/site-meta.ts, data/posts.ts). Every page reads from the same source — when the IRS publishes new numbers in January, one file changes and the entire site updates.

Math is verified, not estimated

Every published example is the exact output of the underlying formula, not a round-number guess. Worked examples on the home page use FV = PV·(1+r)ⁿ + PMT·((1+r)ⁿ−1)/r solved at 7% real return; outputs are rounded to the nearest dollar/year that the formula actually produces.

Conservative defaults

When choices arise — withdrawal rate, return assumption, market-cycle data — we default to the more conservative published value. Trinity 4% rule is the headline; modern 3.3-3.8% guidance is surfaced as an alternative, not buried.

Update cadence

How often each kind of content gets reviewed and refreshed.

Each January

IRS contribution limits (HSA, 401(k), IRA, catch-up) updated in data/contribution-limits.ts; CURRENT_TAX_YEAR bumped; current-year references across the site refresh on next deploy.

When new research lands

Withdrawal-rate guidance and methodology pages updated when major papers publish — currently anchored to Trinity 1998, with Pfau (2010+), Bengen (1994 and updates), and Morningstar's annual SWR research as living references.

Continuously

Reader feedback flagging unclear language or wrong numbers triggers same-week updates. Email contact@financialfirecalculators.com to flag anything.

Per article

Each blog post displays a Last updated date pulled from the post registry. When we materially update a post we bump dateModified in data/posts.ts; structured data (BlogPosting) reflects the new date for search engines.

Primary sources we cite

  • Trinity Study (1998). Cooley, Hubbard & Walz at Trinity University in San Antonio, Texas. "Retirement Savings: Choosing a Withdrawal Rate That Is Sustainable." AAII Journal, February 1998. The empirical basis for the 4% rule.
  • Bengen (1994). William P. Bengen, "Determining Withdrawal Rates Using Historical Data," Journal of Financial Planning. The original 4% safe withdrawal rate paper.
  • Mr. Money Mustache (2012). "The Shockingly Simple Math Behind Early Retirement". The canonical savings-rate-to-years-of-FIRE table used in our reference content.
  • IRS Revenue Procedures. Annual cost-of-living adjustments for HSA, 401(k), IRA contribution limits. We update data/contribution-limits.ts each January.
  • Wade Pfau, Morningstar SWR research. Modern updates to the safe withdrawal rate informing our 3.0%/3.5%/4.5% slider on the 4% rule calculator.
  • Shiller historical S&P 500 data. Used for nominal/real return assumptions and for the Monte Carlo simulator's historical-cycle anchor.

Honest limitations

What this site is not, and where you should look beyond it for personalized advice.

  • We are not a Certified Financial Planner. This site is educational. The author is a software engineer who built these tools to model his own FIRE journey, not a registered investment advisor.
  • All projections are deterministic compound-interest math. Real markets have sequence-of-returns risk, taxes, regulatory change, healthcare inflation, and personal life events that math cannot model.
  • US-centric assumptions: 4% rule is based on US stock and bond returns; tax-advantaged accounts (401(k), IRA, HSA) are US-specific. International readers should treat the framework as transferable but the numbers as US.
  • Monte Carlo simulation runs at 1,000 paths with normally-distributed returns. This is a useful range-of-outcomes estimate, not a prediction.

For personalized financial planning, find a fiduciary planner via NAPFA or the CFP Board.

Editorial owner: Mark S. — Software Engineer, Denver, Colorado.

This page last reviewed: 2026-05 (2026 editorial cycle).

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