Free Online Health Calculators

Health information is everywhere online, but most of it is either locked behind an app requiring a subscription, buried under ads and pop-ups asking for your email, or built around branded products trying to sell you something. The tools in this collection are none of those things. Every calculator here runs directly in your browser, requires no sign-in, and sends nothing to a server. Your height, weight, age, and any other inputs you provide stay on your device and are discarded the moment you close the tab.

Each tool is built around formulas that appear in peer-reviewed literature or are published by recognized health organizations. The BMI Calculator uses the standard World Health Organization definition. The Calorie Calculator is based on the Mifflin-St Jeor equation, which large systematic reviews have found to be the most accurate resting metabolic rate predictor for the general population. The Body Fat Calculator implements the US Navy circumference method alongside the BMI-based Deurenberg formula and a skinfold estimation, so you can compare three independent approaches and understand where they agree and where they diverge. The Heart Rate Zone Calculator uses Karvonen's formula, which accounts for your resting heart rate to give personalized training zones rather than rough age-based approximations. The Ideal Weight Calculator presents four published formulas side by side — Robinson, Miller, Hamwi, and Devine — because no single formula is authoritative for all body types.

The sleep and hydration calculators address something most health apps ignore: the mechanics of rest and recovery. The Sleep Calculator works backward from sleep cycles — because waking at the end of a 90-minute cycle feels dramatically different from waking mid-cycle — to give you concrete bedtimes and wake-up windows. The Water Intake Calculator adjusts your baseline hydration goal by body weight, activity level, and climate, because a sedentary adult in a cool office and an endurance athlete training in summer heat have genuinely different requirements.

The Exercise Finder takes a different approach entirely. Rather than asking you to name a muscle group, it presents an interactive body map: click any region and you get a list of exercises that target it, with difficulty ratings, equipment requirements, form cues, and common technique tips. It covers 120+ exercises across all major muscle groups and works equally well for gym beginners building their first program and experienced lifters looking for targeted accessory work.

The Pregnancy Calculator rounds out the collection. It accepts either a last menstrual period date or a known conception date, then returns the estimated due date, current gestational week, current trimester, and key milestone dates across the full 40-week timeline. As with every tool here, this is an informational estimate; your healthcare provider's ultrasound-based dating takes precedence for clinical decisions.

All nine tools are free, open without any account, and work on any modern browser on phone, tablet, or desktop. If you are a healthcare student, a fitness coach working with clients, a parent tracking a pregnancy, or someone simply trying to understand their own numbers better, this collection covers the most common general health calculations in one place.