InstaCalcs

Health Calculators

Estimate health numbers quickly, then treat them like estimates. Bodies are not spreadsheets.

Health numbers need context

BMI, calories, body fat, water intake, and due dates are useful numbers. They are also rough numbers. Your age, activity level, medical history, cycle length, medications, and genetics can all change the answer.

Use these calculators to get oriented: a starting calorie target, a BMI category, an estimated fertile window, or a bedtime that lines up with sleep cycles. Then adjust based on real life and, for anything medical, talk with a clinician.

The best use is trend tracking. One number can be noisy. A pattern over a few weeks is usually more useful.

Common questions

What is BMI and is it a good measure of health?
BMI compares weight with height. It is useful as a screening tool, but it cannot tell muscle from fat. A very muscular person can land in a high BMI category while still being healthy.
How many calories do I actually need per day?
Daily calorie needs depend on age, sex, height, weight, and activity level. The calculator gives you a starting estimate. If your weight does not move the way you expect after a few weeks, adjust the target.
How much water should I drink daily?
The "8 glasses a day" rule is easy to remember, but it is not personal. Body size, heat, exercise, pregnancy, and some health conditions change fluid needs.
What does body fat percentage tell you?
Body fat percentage estimates how much of your body weight is fat tissue. The Navy method uses tape measurements, so it is not as precise as a lab test. It can still be useful if you measure the same way each time.