Health & Fitness Calculators
BMI, calories, training loads, and pregnancy dates: evidence-based health calculators that are honest about what estimates can and can't tell you.
Body & Nutrition 7
- BMI CalculatorBody mass index with your healthy weight range.
- TDEE CalculatorYour daily calorie burn, plus cut and bulk targets.
- BMR CalculatorCalories you burn at complete rest, with three formulas compared.
- Calorie CalculatorYour daily calorie target for losing, maintaining, or gaining weight.
- Macro CalculatorSplit your calories into protein, carb, and fat grams.
- Weight Loss Rate CalculatorYour pace of weight loss, compared against published guidelines.
- One Rep Max CalculatorEstimate your 1RM from any rep set, with a %1RM chart.
Pregnancy & Cycles 4
- Due Date CalculatorEstimated due date from LMP, conception, or IVF, plus milestone dates.
- Naegele's Rule CalculatorThe classic +7 days, -3 months, +1 year EDD rule, shown step by step.
- Ovulation CalculatorYour estimated ovulation date and fertile window from your cycle dates.
- Period CalculatorWhen your next period is due, with a six-cycle forecast and ovulation days.
Sleep & Longevity 3
Clinical & Fitness Tests 3
More tools 1
Which health calculator do you need?
- Body composition screening. BMI for the standard screening ratio, with the healthy weight range for your height.
- Calories. BMR is what your body burns at rest, TDEE adds your activity to give a daily total, and the macro calculator splits that total into protein, carbohydrate, and fat.
- Changing weight. The weight loss rate calculator works from a deficit to a realistic timeline rather than a flattering one.
- Training. one rep max estimates your ceiling from a set you have actually done.
- Cycle and pregnancy. period and ovulation for cycle tracking, due date and Naegele's rule for pregnancy dating.
- Other. sleep works backwards from when you need to wake, BAC estimates blood alcohol, and the longevity planning calculator is built for retirement planning rather than for predicting anyone's life.
What these numbers can and cannot do
Every calculator on this page is a screening estimate built from population averages. That is genuinely useful for orientation and useless as a diagnosis. BMI measures mass against height and cannot tell muscle from fat, which is why a lean athlete can register as overweight. BMR and TDEE come from equations fitted to groups, and individual metabolisms vary by more than most people expect. A BAC estimate cannot account for what you ate, your medication, or how your body processes alcohol tonight, and it is never a reason to decide you are fit to drive.
Where a result sits near a category boundary, treat the boundary as fuzzy rather than sharp. The difference between a BMI of 24.9 and 25.0 is not a change in your health, it is a change in which label a table applies to you.
Why we show the formula
These pages state the equation, walk a worked example, and name the source the thresholds come from. That is partly so you can check us, and partly because knowing that BMI is just weight divided by height squared makes it much harder to over-read. A number you understand the construction of is a number you can hold at the right distance.
None of this is medical advice, and we say so on every page rather than in the small print. If a result concerns you, or you are an athlete, an older adult, pregnant, or managing a condition, the useful next step is a conversation with a clinician who can see more than a height and a weight.
Frequently asked questions
Is BMI accurate for everyone?
No, and it is not meant to be. BMI is a population-level screening ratio that measures mass against height, so it cannot distinguish muscle from fat. Muscular people often register as overweight while being lean, and it can understate body fat in older adults. It also ignores where fat is carried, which matters clinically. Treat it as a first-pass screen and use waist measurement or body composition for a fuller picture.
Why do BMR and TDEE calculators disagree with each other?
Because they use different equations fitted to different populations. Our BMR and TDEE pages use the Mifflin-St Jeor equation, which is the one most commonly recommended for general use, and we cite the original 1990 paper. Individual metabolic rates vary meaningfully around any equation's prediction, so use the number as a starting point and adjust based on what actually happens over a few weeks.
Can I rely on the BAC calculator to decide whether to drive?
No. Never. A BAC estimate cannot account for what you have eaten, your medications, your rate of drinking, or how your body is processing alcohol tonight, and the real figure can be considerably higher than an estimate. The only safe answer after drinking is not to drive. The calculator exists to show how quickly BAC accumulates, not to certify anyone as fit.
Are these calculators medical advice?
No. Everything here is for general information and education, and none of it substitutes for professional diagnosis or treatment. Every health page carries that notice directly rather than burying it. If a result worries you, or your situation is unusual in any way, talk to a qualified healthcare provider.