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Health Calculator

BMI, daily calories (BMR/TDEE) and pregnancy due date estimates.

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Frequently asked questions

How is BMI calculated?

BMI is your weight in kilograms divided by your height in metres squared. The tool also shows the standard category your result falls into (underweight, normal, overweight, obese). The BMI formula is the same worldwide and is used by health organizations as a simple screening tool for potential weight-related health risks. Enter your height and weight in either metric or imperial units and the calculator instantly shows your BMI and its category. Keep in mind BMI doesn't account for muscle mass, bone density, or age, so it's a general guideline rather than a precise measure of health.

What are BMR and TDEE?

BMR is the calories your body burns at rest; TDEE multiplies that by an activity factor to estimate your total daily calorie needs using the Mifflin–St Jeor equation. BMR (Basal Metabolic Rate) represents the minimum calories needed for basic functions like breathing and circulation, while TDEE (Total Daily Energy Expenditure) accounts for exercise and daily activities on top of BMR. The Mifflin–St Jeor formula is a well-researched, accurate method for estimating TDEE based on age, gender, height, weight, and activity level. Knowing your TDEE helps you set realistic calorie targets for weight loss (eat less than TDEE) or weight gain (eat more than TDEE).

Is this medical advice?

No. The results are general estimates for information only. Always consult a qualified healthcare professional for medical decisions. BMI, BMR, TDEE, and estimated due dates are statistical averages that don't account for individual metabolic differences, medical conditions, or pregnancy complications. These calculations are tools for general guidance and self-awareness, not replacements for professional medical evaluation. If you have concerns about your health, weight, or pregnancy, discuss your specific situation with a doctor or healthcare provider who can account for your unique circumstances.

How is the due date estimated?

Using Naegele's rule, the standard clinical convention: 280 days (40 weeks) from the first day of the last menstrual period, which assumes a 28-day cycle with ovulation on day 14. Enter a longer or shorter usual cycle and the estimate moves by the difference, as clinical calculators do. Irregular cycles still shift the true date, which is one reason a first-trimester dating scan — the more accurate method — routinely revises this estimate. Treat the result as the centre of a window, not an appointment.

Pro tips

  • Read BMI alongside a waist measurement rather than alone — distribution carries more information about risk than the ratio does.
  • Recalculate your calorie estimate after any real change in activity or weight; the figure drifts as the inputs do.
  • Be honest about activity level, and if unsure pick the lower option. Overstating it is the most common reason a calorie target does not produce the expected result.
  • Track outcomes for two to three weeks before adjusting. Day-to-day weight moves with water and food volume far more than with fat.
  • Treat a due-date estimate as a range. Only a small minority of births occur on the predicted day, and dating scans routinely revise it.

About Health Calculator

BMI is a population screening figure and carries no information about body composition, so it misreads muscular and older bodies in opposite directions. All three outputs are estimates for planning, not a substitute for a clinician.

Estimate your Body Mass Index, daily calorie needs using the proven Mifflin–St Jeor formula, and a pregnancy due date from your last menstrual period. It brings three common health estimates together so you can plan diet, fitness and milestones quickly.

These figures are informational estimates rather than medical advice — take decisions about your health with a clinician. Calorie targets especially are a starting point to adjust against real results, since activity level is self-reported and easy to overstate.

Body Mass Index is weight divided by height squared, devised in the 1830s to describe populations rather than individuals — and it remains genuinely useful for the former while being consistently crude for the latter. It cannot distinguish what the weight is made of, so a well-trained athlete routinely registers as overweight while carrying very little fat. It takes no account of where fat sits, which is the part most closely associated with risk, and the height-squared relationship holds poorly at the extremes of height, misreading very tall and very short people in opposite directions.

The calorie figures are two estimates stacked on each other. Basal metabolic rate is predicted from formulas fitted to study populations, and individual rates vary meaningfully around that prediction; multiplying by an activity factor to reach a daily total adds a second approximation, and activity level is self-reported, which people overstate reliably. Treat the result as a starting figure to adjust against what actually happens over a few weeks rather than a target to hit precisely.

Common use cases

  • Getting a rough baseline before a conversation with a GP, dietitian or trainer.
  • Setting an initial calorie target at the start of a training or nutrition plan.
  • Checking where a BMI figure falls when a form, insurer or programme asks for one.
  • Estimating a due date from a last menstrual period while waiting for a dating scan.
  • Understanding what a number quoted in a health article actually measures before drawing conclusions from it.
How it comparesThe NHS and Mayo Clinic calculators come with far better contextual guidance and are the right reference for anything you intend to act on. Bundling the three estimates is convenient for a quick baseline; neither this nor any calculator replaces someone who can examine you.