MoneyMath

About MoneyMath

Last updated

What this site is

MoneyMath is a small but growing network of personal-finance calculators. Fourteen calculators are live across three categories: FIRE math (Coast / Standard / Lean / Barista FIRE), income & wealth (Net Worth, Savings Rate, True Hourly Wage, Freelance Hourly Rate, eBay Profit Margin), and debt & costs (Debt Payoff, Mortgage, Student Loan, True Cost of Car, Lifetime Cost). Each is paired, where it makes sense, with a long-form cornerstone explaining the math from first principles.

The site exists for one reason: most personal-finance calculators on the internet hide their math behind opaque interfaces or, worse, manipulate inputs to push the user toward a specific product. MoneyMath shows the formula, explains its assumptions, and runs in the user’s browser — no server, no account, no telemetry beyond aggregate page-view counts via Cloudflare Web Analytics.

What it isn’t

  • Not financial advice. Outputs depend entirely on the assumptions you provide. Talk to a fiduciary fee-only advisor before any decision worth more than a year of saving.
  • Not a SaaS. No accounts. No subscription required to use the calculators. Inputs save to your device’s localStorage, nothing else.
  • Not AI-generated. Every calculation is hand-derived from first principles. Every explanation is hand-written. Editorial choices are made by a human.
  • Not affiliated with any financial-services company beyond standard, clearly-labeled affiliate relationships (see “How it stays free” below).

Editorial principles

The same five rules apply to every calculator and every guide on this site:

  1. Show the formula. If a calculator returns a number, the math producing that number is shown explicitly somewhere on the page — usually in the long-form guide attached to it. No black boxes.
  2. Cite primary sources. USDA reports, IRS publications, Federal Reserve data, peer-reviewed studies (e.g., Kellogg School of Management’s 2012 work on debt-payoff completion rates). When a number comes from somewhere, that somewhere is named.
  3. Acknowledge what the formula misses. Every guide ends with a section on what the math does not capture: opportunity cost, sequence-of-returns risk, lifestyle creep, life events, behavioral factors. Numerical precision without acknowledged uncertainty is misleading.
  4. No outcome promises. “Retire by 40”, “$1M in 10 years”, “guaranteed” — these don’t appear anywhere on the site, ever. The math gives a target. Whether you hit it depends on choices and circumstances neither the calculator nor we can predict.
  5. Sponsored content is labeled and walled off from the math. Affiliate links to brokerages, robo-advisors, lenders, and similar products are disclosed with rel="sponsored nofollow" and a footer-wide affiliate-disclosure block. The math and product recommendations are independent: a partnership doesn’t change the formula, the assumptions, or the conclusion.

Errata and corrections

Every page on this site is technically a hypothesis. Math errors, broken assumptions, outdated regulations, regional inaccuracies — they happen. If you find one, email hello@m-calculate.com with the URL and the issue. Corrections are made within a week, usually within 24 hours, and acknowledged in a public corrections log when the change is non-trivial.

How content is created

The workflow for a new calculator:

  1. Identify a personal-finance question that’s frequently asked but poorly answered by existing calculators
  2. Derive the math from first principles. Cross-check against published formulas (textbooks, academic papers, official documentation)
  3. Build the calculator as a pure-function library with unit tests. Every calculator has 15+ test cases verifying boundary conditions, edge cases, and reconciliation properties (e.g., breakeven inputs return zero net result)
  4. Write the long-form guide explaining the formula, its assumptions, worked examples, and what it doesn’t capture
  5. Publish

The same workflow applies to revisions. When a regulation changes (e.g., eBay’s fee structure update in 2021, Homeowners Protection Act PMI rules), the affected calculator’s math is updated, the guide is revised, and updatedDate reflects the change.

How it stays free

Three revenue streams, all clearly disclosed:

  1. Display advertising. Google AdSense — small inline + footer placements, no interstitials, no autoplay video, no fake “you have a virus” garbage. We’ve configured AdSense to show only contextually-appropriate finance advertising; if you spot something off, email us.
  2. Affiliate links to financial products we’d consider using ourselves: brokerages (Empower, M1 Finance), robo-advisors (Wealthfront, Betterment), credit-card balance-transfer offers, similar. Marked rel="sponsored nofollow" per FTC guidance. The math doesn’t change based on whether a partner pays us; we link to a product because the math suggests it’s a reasonable option for someone in a given situation, not because of the commission.
  3. Premium tier (planned, not live yet). Future paid tier with PDF export, multiple-scenario saving, ad-free experience. Free tier remains free permanently for the existing calculators. Premium will be locked behind reaching real KPI traction (newsletter subscribers, organic visitors, AdSense revenue) before being built.

Who runs this

MoneyMath is run by a small editorial team operating under the brand name. Communications go to hello@m-calculate.com. We don’t publish individual bylines — every piece reflects the same editorial standards above and is the responsibility of the publication, not an individual author.

If you want to suggest a calculator, report an error, or partner on content, email is the right channel. Replies typically arrive within 48 hours.