What health calculators does Texterfly offer?

Texterfly offers 3 free health calculators: a BMI Calculator (adult and child/teen modes, visual gauge, healthy weight range), a Calorie & Macro Calculator (Mifflin-St Jeor and Katch-McArdle formulas, macronutrient breakdown, goal-based timeline), and a Pregnancy Due Date Calculator (last menstrual period or conception date methods, trimester guide, weekly development milestones). All are for informational purposes only.

What do the BMI categories mean?

BMI (Body Mass Index) categories for adults are: Underweight (below 18.5), Normal weight (18.5–24.9), Overweight (25–29.9), Obese Class I (30–34.9), Obese Class II (35–39.9), and Obese Class III (40 and above). Note that BMI has significant limitations — it does not account for muscle mass, bone density, age, sex, or ethnicity. Athletes may have a high BMI due to muscle, not fat. Always consult a healthcare professional for a full health assessment.

What is the Mifflin-St Jeor formula?

The Mifflin-St Jeor formula estimates Basal Metabolic Rate (BMR) — calories burned at rest. For men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5. For women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161. Multiplying BMR by an activity factor gives TDEE (Total Daily Energy Expenditure), which is the estimated number of calories needed to maintain current weight.

TDEE (Total Daily Energy Expenditure) is the estimated total number of calories you burn per day, including physical activity. It is calculated by multiplying your BMR (Basal Metabolic Rate) by an activity factor: Sedentary (×1.2), Lightly active (×1.375), Moderately active (×1.55), Very active (×1.725), Extra active (×1.9). To lose weight, eat fewer calories than your TDEE; to gain, eat more.

How is a pregnancy due date calculated?

The most common method is Naegele's rule: add 280 days (40 weeks) to the first day of your Last Menstrual Period (LMP). For example, if your LMP was January 1, the estimated due date is October 8. Alternatively, add 266 days to a known conception date. Only about 5% of babies are born on their exact due date — it's an estimate within a 2-week window.

What are the pregnancy trimesters?

First Trimester: Weeks 1–12 (months 1–3). Key developments: fertilisation, heart formation, organ development. Second Trimester: Weeks 13–26 (months 4–6). Key developments: movement felt, sex identifiable, rapid growth. Third Trimester: Weeks 27–40+ (months 7–9+). Key developments: lungs mature, weight gain, preparation for birth.

Are these calculators a substitute for medical advice?

No. These calculators are for informational and educational purposes only. They are not designed to diagnose, treat, cure, or prevent any medical condition. BMI, calorie needs, and pregnancy timelines are estimates based on statistical formulas — individual health varies significantly. Always consult a qualified healthcare professional, doctor, or registered dietitian for personalised medical guidance.

How accurate is the BMI calculator?

The BMI formula is mathematically accurate — it correctly calculates weight (kg) divided by height (m²). However, BMI as a health metric has well-documented limitations: it does not distinguish between fat and muscle, does not account for where fat is stored (visceral vs subcutaneous), and may misclassify athletes as overweight and elderly people with muscle loss as normal weight. Use BMI as one data point, not a definitive measure of health.

Are these health calculators free?

Yes. All 3 health calculators are 100% free with no registration, subscription, or payment required.

Is my health data private?

Yes. All calculations run entirely in your browser. Your weight, height, age, activity level, and other personal health data are never sent to any server or stored anywhere.

What is a healthy BMI?

For adults, the WHO defines the healthy BMI range as 18.5–24.9. Below 18.5 is underweight. 25–29.9 is pre-obese (overweight). 30–34.9 is Obese Class I. 35–39.9 is Obese Class II. 40 or above is Obese Class III.

How is BMI calculated?

BMI = weight in kg ÷ (height in metres)². In imperial: BMI = (weight in lbs × 703) ÷ (height in inches)². Example: 70 kg at 1.75 m → BMI = 70 ÷ 3.0625 = 22.9.

What is a healthy BMI for women?

The standard healthy BMI for adult women is 18.5–24.9. However, some research suggests the optimal range may be slightly lower (18.5–23) for women of Asian descent.

What is a healthy BMI for men?

For adult men, a healthy BMI is 18.5–24.9. Heavily muscled athletes may fall in the overweight range (25–30) despite low body fat, so context matters.

How is BMI for children different?

For children ages 2–20, BMI is interpreted using age- and sex-specific CDC percentile charts, not fixed adult thresholds. Under 5th percentile = underweight, 5th–84th = healthy weight, 85th–94th = overweight, 95th or above = obese.

BMI is a useful population screening tool but has limitations. It does not measure body fat directly and cannot distinguish between muscle and fat. Athletes may have a high BMI despite low body fat. It should be used alongside waist circumference, body fat %, and clinical assessment.

BMI Prime is your BMI divided by 25 (the upper limit of the normal range). A value below 1.0 is healthy, exactly 1.0 is at the top of the normal range, above 1.0 is overweight. It shows at a glance how close to or far from the healthy upper limit you are.

Does this BMI calculator store my data?

No. All calculations run entirely in your browser. No personal health data is ever sent to or stored on any server.

Back to Health & Fitness

BMI Calculator

Calculate your Body Mass Index instantly. Visual gauge, WHO categories, healthy weight range, BMI Prime, and weight scenarios. Separate child mode with CDC percentiles for ages 2–20.

Adult BMIChild & Teen PercentileBMI PrimeHealthy Weight RangeVisual GaugeMetric & ImperialReal-Time100% Free

BMI Calculator

Mode

Units

Height (cm)

Weight (kg)

Quick examples

WHO BMI Classification

Category	BMI Range
Severe Thinness	0 – 16
Moderate Thinness	16 – 17
Mild Thinness	17 – 18.5
Normal Weight	18.5 – 25
Pre-Obese	25 – 30
Obese Class I	30 – 35
Obese Class II	35 – 40
Obese Class III	≥ 40

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Enter your height and weight to see your BMI result, gauge, and healthy weight range.

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What Is BMI?

Body Mass Index (BMI) is a numerical value derived from a person's height and weight. It is the most widely used screening tool for categorising weight status and identifying potential health risks associated with being underweight, overweight, or obese.

# BMI Formula

Metric: BMI = weight (kg) ÷ height (m)²

Imperial: BMI = (weight (lbs) × 703) ÷ height (in)²

# Example: 70kg, 175cm

BMI = 70 ÷ (1.75)² = 70 ÷ 3.0625 = 22.9

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Visual Gauge

See exactly where your BMI sits on a colour-coded gauge from underweight (blue) to healthy (green) to obese (red).

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Child Mode

For ages 2–20, BMI is interpreted using CDC percentile charts, not adult thresholds — this tool uses age and sex for an accurate child result.

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Weight Scenarios

See how your BMI and category change at ±5 and ±10 kg — so you know exactly how much change is needed to reach a healthy range.

BMI Chart by Age — Adults

WHO thresholds apply to all adults (18+). Note: some health bodies recommend lower thresholds for Asian populations (23 = overweight).

BMI Range	WHO Category	Health Risk	Action
< 16	Severe Thinness	Very high	Medical evaluation required
16 – 17	Moderate Thinness	High	Clinical assessment recommended
17 – 18.5	Mild Thinness	Moderate	Monitor and improve nutrition
18.5 – 25	Normal Weight	Low	Maintain healthy lifestyle
25 – 30	Pre-Obese	Increased	Improve diet and increase activity
30 – 35	Obese Class I	High	Weight management program
35 – 40	Obese Class II	Very high	Medical support recommended
≥ 40	Obese Class III	Extremely high	Specialist medical care

Frequently Asked Questions

What is BMI?: Body Mass Index (BMI) is a simple calculation using height and weight: BMI = weight (kg) ÷ height (m)². It was developed in the 1830s by Belgian statistician Adolphe Quetelet and is used worldwide as a quick screening tool for weight-related health risks.
What is a healthy BMI?: For adults, the WHO defines the healthy BMI range as 18.5–24.9. Below 18.5 is underweight, 25–29.9 is pre-obese (commonly called overweight), 30–34.9 is Obese Class I, 35–39.9 is Obese Class II, and 40+ is Obese Class III.
Is BMI an accurate measure of health?: BMI is a useful population-level screening tool, but has well-known limitations. It does not distinguish between fat and muscle mass, so heavily muscled athletes may be classified as overweight. It also doesn't account for fat distribution, age, or ethnicity. It should be used alongside other measurements like waist circumference, body fat %, and clinical assessment.
What is a healthy BMI for women?: The standard healthy BMI range for adult women is 18.5–24.9, identical to men. However, women naturally carry more body fat than men at the same BMI. Some research suggests the optimal BMI range for health outcomes may be slightly lower (18.5–23) for women of Asian descent.
What is a healthy BMI for men?: For adult men, a healthy BMI is 18.5–24.9. Men typically carry less body fat at a given BMI than women, and muscle-heavy athletes may have a BMI in the overweight range (25–29.9) despite very low body fat. Context and body composition matter more than the number alone.
How is BMI calculated?: BMI = weight in kg ÷ (height in metres)². Example: A person weighing 70 kg at 1.75 m has BMI = 70 ÷ (1.75)² = 70 ÷ 3.0625 = 22.9. In imperial: BMI = (weight in lbs × 703) ÷ (height in inches)².
How is child and teen BMI different?: For children ages 2–20, BMI is not interpreted using fixed adult thresholds. Instead, it is plotted against age- and sex-specific percentile charts (CDC growth charts). Underweight = below 5th percentile, Healthy = 5th–84th, Overweight = 85th–94th, Obese = 95th percentile or above. This is because healthy BMI changes significantly as children grow.
Can I have a high BMI and still be healthy?: Yes. Well-trained athletes and bodybuilders often have BMIs in the overweight range (25–30) due to high muscle mass, not excess fat. Conversely, someone with a "normal" BMI can still carry unhealthy levels of visceral fat. This is why BMI is a screening tool, not a diagnosis. Waist-to-height ratio and body fat percentage are more accurate complementary measurements.
What is a BMI prime?: BMI Prime is your BMI divided by 25 (the upper limit of the normal range). A BMI of 22 has a BMI Prime of 0.88. Values below 0.74 are underweight, 0.74–1.00 is normal, above 1.00 is overweight. It gives a quick sense of how far above or below the healthy upper limit you are.
Does this calculator store my data?: No. All calculations run entirely in your browser using JavaScript. No personal health data is ever sent to or stored on any server.

Medical Disclaimer: This BMI calculator is for informational purposes only and does not constitute medical advice. BMI is a screening tool, not a diagnostic measure. Consult a qualified healthcare professional for a personalised health assessment.

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