Methodology & Sources

CalcNimbus exists to give clear, correct answers, so every calculator here is built on a recognized formula, checked by hand, and tied to an authoritative source. This page explains exactly how we do that and where the numbers come from.

How we build and check every calculator

1. Start from the standard method. We don't invent formulas. Each tool implements the established method for its topic — the Mifflin-St Jeor equation for resting calories, the amortization formula for loan payments, the IOM guidelines for pregnancy weight gain, and so on.
2. Verify by hand. Every formula is re-derived by hand against a worked example before it goes live. If the calculator and the hand calculation don't agree to the cent, it doesn't ship.
3. Use real US units and examples. Dollars, miles, pounds, Fahrenheit, the 4.0 GPA scale, current IRS brackets — the inputs, defaults and examples match how things actually work in the United States.
4. Show the work. Each page includes the formula, worked examples, common mistakes and FAQs, so you can see how the result was reached, not just the number.
5. Review and update. Tools are reviewed for accuracy and refreshed when the underlying rules change — for example, new tax brackets each year.

All of this is built and personally checked by Jeferson Bruno, the developer and editor behind CalcNimbus.

Our sources, by topic

• Taxes & paychecks: the Internal Revenue Service (IRS) for brackets, the standard deduction and FICA rates; the Social Security Administration; and state departments of revenue.
• Mortgages & loans: the Consumer Financial Protection Bureau (CFPB), Freddie Mac, and the Federal Reserve.
• Investing & retirement: the IRS (including the SECURE 2.0 Act for RMDs), the U.S. Securities and Exchange Commission, and the Bureau of Labor Statistics for inflation (CPI).
• Health & fitness: the Mifflin-St Jeor equation, the U.S. Navy circumference (tape) method for body fat, and guidance from the CDC and NIH.
• Pregnancy & baby: the American College of Obstetricians and Gynecologists (ACOG), the Institute of Medicine (IOM) 2009 weight-gain guidelines, the CDC for breast-milk storage, and the USDA for the cost of raising a child.
• Construction & home: manufacturer mix-yield standards for concrete, the International Residential Code (IRC) for stairs, the U.S. Department of Energy for insulation R-values, and ADA guidance for ramp slope.
• Education: the standard US 4.0 GPA scale and College Board conventions for weighted (AP/Honors) grades.
• Unit conversions: the National Institute of Standards and Technology (NIST).

Accuracy and corrections

We work hard to keep every calculator accurate, but rules change and mistakes can happen. If you spot a number that looks wrong, please tell us — we review every report and correct errors quickly.

Important disclaimer

CalcNimbus's calculators are informational tools, not professional advice. They produce estimates to help you understand a topic and plan; they are not a substitute for a qualified accountant, financial advisor, physician, attorney or other professional. Always confirm important decisions with a licensed expert.

Last updated: June 19, 2026.