FitCalcTools provides free, science-based calculators for health, fitness, and personal finance. Every tool on this site uses peer-reviewed formulas and transparent methodology — no black boxes, no guesswork.
Our formulas include: Mifflin-St Jeor and Harris-Benedict equations (BMR/TDEE), U.S. Navy circumference method (body fat), Devine/Robinson/Miller/Hamwi formulas (ideal weight), Widmark formula (blood alcohol content), Epley/Brzycki/Lombardi equations (one-rep max), Karvonen method (heart rate zones), and Naegele's Rule (pregnancy due date). Financial calculators use standard compound interest, amortization, and budget allocation formulas.
We believe useful tools should be fast, clean, and accessible to everyone without requiring an account, a download, or a payment.
Our calculators cover sleep optimization (based on 90-minute sleep cycles), body composition (body fat, ideal weight, BMR), nutrition planning (macronutrient targets), hydration needs, and compound interest projections.
Each calculator includes detailed explanations of the underlying science, FAQs, and structured data for search engines. We aim to be the most accurate and user-friendly calculator site on the web.
Ellis Hartley — Founder and editor of FitCalcTools.
I built this site because most online calculators hand you a number without telling you which formula produced it or where that formula came from, which makes the result impossible to check. Every tool here names the formula it uses and cites the guideline, dataset, or peer-reviewed study that defines it, so you can see exactly what produced the number rather than taking a black box on trust.
I am not a physician, a registered dietitian, or a licensed financial adviser, and nothing on this site is personalised advice. What I do is research the primary sources, implement the published equations, and state plainly where a formula stops being reliable. On the calculators where more than one accepted equation is in common use — BMR, TDEE, ideal weight, lean body mass, one-rep max — the page shows the spread instead of picking one and hiding the rest.
Corrections and questions: hello@fitcalctools.com
Contact: hello@fitcalctools.com
Every formula is sourced. Each calculator page carries a Sources & methodology section listing the specific guideline, government dataset, or peer-reviewed paper the numbers come from, with a direct link. We cite primary sources — the National Academies, the CDC, the WHO, ACOG, the IRS, the Federal Reserve, the CFPB, the FDIC, and indexed journals — not other calculator sites.
Every page shows when it was last reviewed. Guidelines change: contribution limits are updated annually, deposit and mortgage rates move monthly, and clinical recommendations are revised. When an underlying source is revised, the affected pages are re-checked and their review date updated.
We show the maths, not a black box. Each page names the formula it uses and links to the published source that defines it, so you can see which equation produced the number and check it against the original. On the BMR, TDEE, ideal weight, lean body mass and one-rep max calculators, several accepted formulas exist — Mifflin-St Jeor versus Harris-Benedict, or Devine versus Robinson versus Miller versus Hamwi — and those pages run more than one and show the spread, because the disagreement between them is information you should have.
We state the limits. These are population-average formulas. They cannot account for individual medical history, medication, body composition, or financial circumstance. Where a formula is known to be unreliable for a group — BMI for athletes and for some ethnic groups, the Widmark equation for people with liver conditions, the 3,500-kcal rule for sustained weight loss — the page says so.
Corrections. If you find an error, email hello@fitcalctools.com. Corrections are made to the page and the review date is updated.
FitCalcTools is free and carries display advertising through Google AdSense. Advertisers have no input into which calculators we build, what the pages say, or which sources we cite. We do not run sponsored placements, affiliate links, or paid reviews, and no calculator result is influenced by a commercial relationship.
The information provided by FitCalcTools is for educational and informational purposes only. All calculator results are mathematical estimates based on published formulas and population averages. They do not constitute professional medical, financial, legal, or nutritional advice.
Health & medical calculators: Results from our health calculators (BMR, TDEE, body fat, macros, calorie deficit, water intake, sleep, heart rate) are estimates that do not account for individual health conditions, medications, or medical history. Do not use these results to self-diagnose or self-treat any condition. Always consult a qualified healthcare professional before making changes to your diet, exercise, or health regimen. Results do not account for conditions such as diabetes, kidney disease, thyroid disorders, or eating disorders. Pregnant or nursing women, minors, and individuals with pre-existing medical conditions must consult a physician before modifying their diet, exercise, or water intake.
Fertility & pregnancy calculators: Our ovulation calculator and pregnancy due date calculator provide estimates based on average cycle data. They should never be used as a method of birth control or as a substitute for clinical fertility evaluation. Consult your OB-GYN, midwife, or fertility specialist for personalized guidance.
Blood alcohol calculator: BAC estimates are approximations only. Actual blood alcohol levels depend on many individual factors including genetics, medications, food intake, liver function, and hydration. This tool must never be used to determine whether you are safe to drive, operate machinery, or perform any activity requiring alertness. When in doubt, do not drive. If you are concerned about alcohol use, contact SAMHSA's National Helpline at 1-800-662-4357.
Fitness calculators: Our 1RM calculator and other fitness tools provide estimates for training programming. Always use proper form, adequate warm-up, and a qualified spotter when lifting heavy weights. Consult a certified fitness professional before beginning any new exercise program, especially if you have pre-existing injuries or health conditions.
Financial calculators: Our compound interest, budget, debt payoff, salary, and rent vs. buy calculators provide mathematical projections that do not account for taxes, fees, inflation, market conditions, or individual financial circumstances. They do not constitute financial, investment, tax, or legal advice. No fiduciary relationship is established by using our tools. FitCalcTools is not your financial advisor, CPA, attorney, or broker. Users are solely responsible for their financial decisions and any resulting gains or losses. Consult a qualified professional before making financial decisions.
Limitation of liability: FitCalcTools, its creators, and contributors shall not be held liable for any decisions, actions, losses, damages, or injuries resulting from the use of or reliance on any calculator or content on this website. Use all tools at your own risk.
Have feedback, questions, or suggestions for new calculators? We'd love to hear from you.
Email: hello@fitcalctools.com