For informational purposes only. These calculators provide estimates based on statistical formulas and are not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional for health concerns.
Free Health & Fitness Calculators
BMI calculator, daily calorie and macro calculator, and pregnancy due date calculator — all free, instant, and browser-based. Your health data never leaves your device.
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BMI Calculator
Body Mass Index for adults, children & teens
Calculate your Body Mass Index with visual gauge and healthy weight range. Includes both adult mode and child/teen mode (age and sex-adjusted percentiles). Results are displayed with full BMI category context.
- Get a quick snapshot of weight status
- Track progress over a diet or fitness plan
- Check a child's BMI percentile against age norms
Calorie & Macro Calculator
Daily calories, TDEE & macronutrient targets
Estimate your daily calorie needs (TDEE) and macronutrient breakdown for weight loss, maintenance, or muscle gain. Uses the Mifflin-St Jeor formula and adjusts by activity level. Includes goal-based calorie deficit/surplus guidance.
- Find your maintenance calorie level
- Calculate a calorie deficit for weight loss
- Set protein targets for muscle building
Pregnancy Due Date Calculator
Estimated due date, trimesters & milestones
Estimate your baby's due date using your Last Menstrual Period (Naegele's rule) or a known conception date. Includes a full pregnancy timeline, trimester breakdown, and weekly development milestones.
- Estimate your expected due date
- Track which trimester or week you are in
- Understand key development milestones by week
Which Calculator Should I Use?
Match your question to the right tool:
| I need to… | Example | Use this tool |
|---|---|---|
| Check if my weight is in a healthy range | Weight 75 kg, height 175 cm | BMI Calculator |
| Check my child's growth relative to peers | Child, age 10, weight and height | BMI Calculator |
| Find how many calories I need per day | To maintain, lose, or gain weight | Calorie & Macro Calculator |
| Calculate my protein target for muscle gain | Moderately active, 80 kg, goal: muscle | Calorie & Macro Calculator |
| Find my estimated baby due date | LMP was June 1st | Pregnancy Due Date Calculator |
| See what week of pregnancy I am in | Due date is March 15 — what week now? | Pregnancy Due Date Calculator |
BMI Categories Reference
Standard adult BMI categories as defined by the WHO. Note that BMI is a screening tool, not a diagnostic measure — it does not account for muscle mass, age, ethnicity, or fat distribution.
| BMI Range | Category | Notes |
|---|---|---|
| Below 18.5 | Underweight | May indicate nutritional deficiency. Consult a doctor if unintentional. |
| 18.5 – 24.9 | Normal weight | Generally associated with lower risk of weight-related health conditions. |
| 25.0 – 29.9 | Overweight | May indicate increased risk; depends on individual factors like muscle mass. |
| 30.0 – 34.9 | Obese (Class I) | Associated with higher risk of metabolic conditions. Medical guidance recommended. |
| 35.0 – 39.9 | Obese (Class II) | Significantly elevated health risk. Consult a healthcare professional. |
| 40.0 and above | Obese (Class III) | Highest risk category. Medical evaluation strongly recommended. |
Calorie Calculator — Formulas & Activity Levels
The Calorie Calculator uses Mifflin-St Jeor to estimate BMR, then multiplies by your activity factor to get TDEE.
Mifflin-St Jeor Formula
Men BMR
(10 × kg) + (6.25 × cm) − (5 × age) + 5Women BMR
(10 × kg) + (6.25 × cm) − (5 × age) − 161TDEE
BMR × Activity FactorActivity Level Multipliers
| Level | Factor | Example |
|---|---|---|
| Sedentary | ×1.20 | Desk job, little/no exercise |
| Lightly Active | ×1.375 | Light exercise 1–3 days/week |
| Moderately Active | ×1.55 | Moderate exercise 3–5 days/week |
| Very Active | ×1.725 | Hard exercise 6–7 days/week |
| Extra Active | ×1.90 | Physical job + daily training |
🏃 Lose Weight
Eat 300–500 kcal below TDEE for ~0.5 kg/week loss. Avoid drops larger than 1,000 kcal below TDEE.
⚖️ Maintain Weight
Eat at TDEE. Adjust by ±100–200 kcal based on weekly weight trends.
💪 Gain Muscle
Eat 200–400 kcal above TDEE. Prioritise protein at 1.6–2.2 g/kg of bodyweight.
Pregnancy Trimesters — Quick Reference
A pregnancy is approximately 40 weeks from the Last Menstrual Period (LMP), divided into three trimesters. Dates are estimates — confirm with your midwife or OB-GYN.
First Trimester
Weeks 1–12 · Months 1–3
- •Fertilisation and implantation
- •Heart begins beating (week 6)
- •Major organs start forming
- •Risk of miscarriage highest
- •Morning sickness common
Second Trimester
Weeks 13–26 · Months 4–6
- •Movement felt (quickening, ~week 18–22)
- •Sex identifiable by ultrasound
- •Rapid growth and weight gain
- •Most comfortable trimester
- •Anomaly scan typically week 20
Third Trimester
Weeks 27–40+ · Months 7–9+
- •Lungs maturing
- •Significant weight gain for baby
- •Baby moves into head-down position
- •Braxton Hicks contractions
- •Full term at 37–42 weeks
Who Uses These Health Calculators?
Fitness Enthusiasts
Use the Calorie & Macro Calculator to set accurate daily calorie targets and protein goals. Pair with the BMI Calculator to track overall progress alongside body composition changes.
Health-Conscious Individuals
Use the BMI Calculator for periodic weight status check-ins. Use the Calorie Calculator to understand maintenance calories and make informed dietary choices.
Expectant Parents
Use the Pregnancy Due Date Calculator to estimate the arrival date, track which trimester you're in, and explore weekly developmental milestones.
Students & Healthcare Learners
Use the tools to understand how BMI, TDEE, and Naegele's rule work in practice. The formula references and activity level tables provide useful educational context.
Why Use Texterfly Health Calculators?
Scientifically Grounded
Uses validated formulas: Mifflin-St Jeor for calories, WHO BMI categories for weight, and Naegele's rule for pregnancy due dates — the same methods used in clinical settings.
Health Data Stays Private
Your weight, height, age, and other health inputs are processed entirely in your browser. No personal health data is sent to any server or stored.
Works on Any Device
Fully responsive on iOS, Android, desktop, and tablet. No app download, no account. Access from any browser for on-the-go health checks.
Frequently Asked Questions
What health calculators does Texterfly offer?
Three free health calculators: a BMI Calculator (adult and child/teen modes, visual gauge, healthy weight range), a Calorie & Macro Calculator (Mifflin-St Jeor formula, TDEE, macronutrient breakdown, goal-based guidance), and a Pregnancy Due Date Calculator (LMP and conception methods, trimester timeline, weekly milestones). All are for informational purposes only.
What do the BMI categories mean?
Adult BMI categories: 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), Obese Class III (40+). Important: BMI does not account for muscle mass, bone density, age, sex, or fat distribution. Athletes may show as overweight due to muscle. Use BMI as one data point and consult a healthcare professional for a full assessment.
What is the Mifflin-St Jeor formula?
It estimates Basal Metabolic Rate (BMR) — calories burned at rest. Men: BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5. Women: BMR = (10 × kg) + (6.25 × cm) − (5 × age) − 161. Multiplying by an activity factor gives TDEE (Total Daily Energy Expenditure). This is the most widely validated formula for estimating calorie needs in non-clinical settings.
What is TDEE?
TDEE (Total Daily Energy Expenditure) is the estimated total calories burned per day including physical activity. It is BMR × 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 below TDEE; to gain, eat above.
How is a pregnancy due date calculated?
The standard method is Naegele's rule: add 280 days (40 weeks) to the first day of your Last Menstrual Period. Example: LMP January 1 → due date October 8. Using a conception date: add 266 days. Only ~5% of babies are born on their exact due date — it's a statistical estimate within a 2-week window. Confirm dates with your healthcare provider.
What are the three pregnancy trimesters?
First Trimester: Weeks 1–12. Fertilisation, heart formation, organ development. Second Trimester: Weeks 13–26. Movement felt, sex identifiable, rapid growth. Third Trimester: Weeks 27–40+. Lung maturation, significant weight gain, preparation for birth. The Pregnancy Calculator shows which trimester you're in and your current week automatically.
Are these calculators a substitute for medical advice?
No. These tools 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 population-level statistical formulas. Always consult a qualified doctor, midwife, or registered dietitian for personalised guidance.
How accurate is the BMI calculator?
The BMI formula is mathematically exact (weight in kg ÷ height in m²). However, BMI has well-documented limitations as a health metric: it cannot distinguish fat from muscle, does not account for fat distribution (visceral vs subcutaneous), and may misclassify athletes (overweight) and elderly people with muscle loss (normal weight). Use it as one of several health indicators, not a definitive measure.
Are these 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, and other health data are never sent to any server or stored anywhere.