The standard estimate is 280 days (40 weeks) from the first day of the last menstrual period. Only about 5% of babies arrive on their exact due date, it's an estimate, not a deadline.

Basal Metabolic Rate is the number of calories the body burns at complete rest. It's the largest component of daily calorie burn, about 60-75%.

🏃 Health & Fitness

Health & Fitness Calculators

Q: How many calories should I eat to lose weight?

A safe deficit is typically 500 calories below TDEE, producing about 0.5kg (1lb) of weight loss per week. Consult a healthcare professional before starting any significant calorie restriction.

Q: How do I calculate my running pace?

Pace equals time divided by distance. If a run covers 5km in 25 minutes, pace is 5:00 per km.

Q: Are these calculators medically accurate?

They use established, peer-reviewed formulas such as Mifflin-St Jeor for BMR, WHO criteria for BMI, and Naegele's rule for due dates, and provide reliable estimates, though they are not medical devices.

17 free health and fitness calculators for BMI, calories, macros, body fat, FFMI, ideal weight, pregnancy, sleep, hydration and more. Get personalised estimates to support your wellness goals.

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What Are Health & Fitness Calculators?

Health and fitness calculators give you personalised estimates for body composition, nutrition, exercise, sleep, hydration, and reproductive health. They turn your measurements, age, activity level, and goals into actionable numbers — how many calories to eat, how much protein you need, what your healthy weight range is, or when your baby is due. These are screening and planning tools, not medical diagnoses — always consult a healthcare professional for personalised medical advice.

Body Composition Tools

Understanding your body composition helps you set realistic goals and track progress. The BMI calculator estimates whether your weight falls within a healthy range for your height, using the formula endorsed by the World Health Organization. The body fat calculator estimates your body fat percentage using measurements, giving a more nuanced picture than BMI alone. The ideal weight calculator shows healthy weight ranges based on multiple established formulas (Devine, Robinson, Miller, Hamwi). For lifters specifically, the FFMI calculator goes a step further than BMI by calculating Lean Body Mass and Fat-Free Mass Index — a height-normalised measure of muscularity that BMI can’t capture, since BMI doesn’t distinguish muscle from fat.

BMI = Weight (kg) ÷ Height (m)²

BMI Categories (WHO):
Below 18.5 — Underweight
18.5–24.9 — Normal weight
25.0–29.9 — Overweight
30.0+ — Obese

💡 BMI is a useful screening tool but has limitations — it doesn’t distinguish between muscle and fat, so athletes with high muscle mass can be classified as “overweight” despite being very fit. Use it alongside body fat percentage, FFMI, and waist measurements for a fuller picture.

Nutrition & Diet Tools

Nutrition calculators help you plan what and how much to eat based on your body and goals. The BMR calculator estimates your basal metabolic rate — the calories your body burns at rest — using the Mifflin-St Jeor equation. The calorie calculator builds on BMR by factoring in your activity level to estimate your total daily energy expenditure (TDEE), then adjusts for your goal (lose, maintain, or gain weight). The macro calculator breaks that calorie target into grams of protein, carbohydrates, and fat using a fixed ratio. The IIFYM macro calculator takes a different approach — it calculates your calorie target first from your TDEE and goal, then derives gram-based protein, carb, and fat targets from that number, which is the actual “If It Fits Your Macros” methodology used by flexible dieters. The protein calculator gives a focused recommendation for daily protein intake based on your weight and activity level.

Hydration & Sleep

The water intake calculator estimates how much water you should drink daily based on your weight, activity level, and climate. Proper hydration affects energy, digestion, skin, and exercise performance. The sleep calculator works out the best times to go to bed or wake up based on 90-minute sleep cycles, so you wake at the end of a cycle rather than in the middle — which is the difference between feeling refreshed and groggy.

Running & Exercise

The pace calculator converts between pace (minutes per km or mile), speed, and finish time for running, cycling, or swimming. Enter any two values and it calculates the third. It’s essential for race planning — working out the pace you need to hit a target marathon or 5K time, or estimating your finish time at your current training pace.

Pregnancy & Reproductive Health

The pregnancy due date calculator estimates your expected delivery date based on your last menstrual period or conception date, using the standard Naegele’s rule (280 days from the first day of the last period). The ovulation calculator and period and ovulation calculator estimate your fertile window based on your cycle length, helping with family planning — whether you’re trying to conceive or tracking your cycle for awareness.

Important Disclaimer

These calculators provide estimates based on general formulas and population averages. They are not medical advice and should not replace consultation with a doctor, dietitian, or other qualified healthcare professional. Individual needs vary based on medical history, genetics, medications, and conditions that calculators can’t account for. Use these tools for guidance and planning, and seek professional advice for health decisions.

Related Tools

Health and fitness often intersect with other calculations. The age calculator gives your exact age in years, months, and days. The percentage calculator is useful for tracking progress (e.g. body fat percentage changes). The unit converter handles kg-to-lb and cm-to-inch conversions that come up constantly in fitness contexts. And the budget planner can help you allocate funds for gym memberships, supplements, or meal plans.

Frequently Asked Questions

What is a healthy BMI?

The WHO defines a healthy BMI as 18.5–24.9. Below 18.5 is underweight; 25–29.9 is overweight; 30+ is obese. However, BMI doesn’t account for muscle mass or body composition — use it as a starting point alongside other metrics. Check yours with the BMI calculator.

How many calories should I eat to lose weight?

A safe deficit is typically 500 calories below your TDEE, which produces about 0.5 kg (1 lb) of weight loss per week. The calorie calculator estimates your TDEE and suggests targets for weight loss, maintenance, or gain. Consult a healthcare professional before starting any significant calorie restriction.

How much protein do I need per day?

General guidelines suggest 0.8g per kg of body weight for sedentary adults, 1.2–1.6g for active people, and 1.6–2.2g for those building muscle. The protein calculator gives a personalised recommendation based on your weight and activity level.

How much water should I drink daily?

A common guideline is about 2–3 litres for most adults, but needs vary by weight, activity, climate, and diet. The water intake calculator provides a personalised estimate. Note that food provides about 20% of your daily water intake.

When is my baby due?

The standard estimate is 280 days (40 weeks) from the first day of your last menstrual period. The due date calculator computes this for you and shows your current week of pregnancy. Remember that only about 5% of babies arrive on their exact due date — it’s an estimate, not a deadline.

What is BMR?

Basal Metabolic Rate is the number of calories your body burns at complete rest — just to keep your organs functioning, blood circulating, and cells repairing. It’s the largest component of your daily calorie burn (about 60–75%). The BMR calculator estimates yours based on age, sex, height, and weight.

How do I calculate my running pace?

Pace = Time ÷ Distance. If you ran 5 km in 25 minutes, your pace is 5:00 per km. The pace calculator converts between pace, speed, and finish time, and works for running, cycling, and swimming in both metric and imperial units.

What’s the difference between FFMI and BMI?

BMI measures total body weight relative to height and can’t distinguish muscle from fat. FFMI measures only fat-free (lean) mass relative to height, making it a much better indicator of muscularity for people who train. The FFMI calculator uses your body fat percentage to calculate it.

How is IIFYM different from a regular macro calculator?

A regular macro calculator applies a fixed percentage split to a calorie number you already have. The IIFYM calculator calculates your calorie target first from your BMR, activity level, and goal, then derives gram-based protein, carb, and fat targets from that number using evidence-based guidelines.

Are these calculators medically accurate?

They use established, peer-reviewed formulas (Mifflin-St Jeor for BMR, WHO criteria for BMI, Naegele’s rule for due dates) and provide reliable estimates. However, they are not medical devices and don’t account for individual health conditions. Use them for planning and screening, and consult a healthcare professional for medical decisions.

Is my health data private?

Yes. All calculations run in your browser — no weight, measurements, or health data is uploaded, stored, or shared. You can use these tools with your real figures in complete privacy.

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