How the calculator works: the Mifflin-St Jeor formula
The calculator first estimates your basal metabolic rate (BMR): the energy your body uses at complete rest for breathing, circulation and cell repair. It uses the Mifflin-St Jeor equation, which predicts resting energy from your weight, height, age and the sex-specific constants from the original study.1 It does not measure your metabolism, so your real number can differ.
BMR for men = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5
BMR for women = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161
Maintenance calories (TDEE) = BMR × your activity multiplier
Your total daily energy expenditure (TDEE) is your BMR multiplied by an activity factor for daily movement and exercise. It is the number of calories that keeps your weight steady. The goal you choose then adds or takes away a fixed amount.
A systematic review of the common equations found Mifflin-St Jeor the most reliable: it predicted resting energy within 10% of the measured value for more people than the other equations did.2
Who the calculator is for
This tool is for adults aged 18 and over who are not pregnant or breastfeeding. It cannot set your intake for a medical condition or an eating disorder. The activity multipliers and goal adjustments are standard assumptions, not measurements of you. For a model that follows how your energy needs change as your weight changes, try the NIDDK Body Weight Planner.3
Activity multipliers
Your activity level is where most estimates go wrong. The multipliers below are rough assumptions, not values measured from your week. If you are unsure, choose the lower level and adjust after two to four weeks.
| Activity level | Multiplier | What a week looks like |
|---|---|---|
| Mostly sitting | 1.2 | Desk job, car everywhere, no structured exercise |
| Light exercise | 1.375 | Light exercise on one to three days a week |
| Moderate exercise | 1.55 | Moderate exercise on three to five days a week |
| Hard exercise | 1.725 | Hard training on six or seven days a week |
| Very hard training or a physical job | 1.9 | Intense daily training, training twice a day, or a physically demanding job |
Two worked examples
A 30-year-old man, 180 cm and 80 kg, moderate exercise, steady fat loss.
BMR = (10 × 80) + (6.25 × 180) − (5 × 30) + 5 = 800 + 1,125 − 150 + 5 = 1,780 kcal
TDEE = 1,780 × 1.55 = 2,759 kcal
Fat-loss target = 2,759 − 500 = 2,259 kcal a day
A 45-year-old woman, 165 cm and 72 kg, light exercise, steady fat loss.
BMR = (10 × 72) + (6.25 × 165) − (5 × 45) − 161 = 720 + 1,031 − 225 − 161 = 1,365 kcal
TDEE = 1,365 × 1.375 = 1,877 kcal
Fat-loss target = 1,877 − 500 = 1,377 kcal a day
Goal adjustments
Once you know your TDEE, the goal you choose sets your daily target:
| Goal | Daily target | What to know |
|---|---|---|
| Maintain weight | TDEE | Eat at maintenance to hold your weight steady. |
| Fat loss, 300 kcal | TDEE − 300 | A gentle deficit that is easiest to keep through brunches, travel and Ramadan. |
| Fat loss, 500 kcal | TDEE − 500 | The usual starting point. An example adjustment, not a personal prescription; actual weight change varies. |
| Faster loss, 750 kcal | TDEE − 750 | Raises the risk of losing muscle, energy and mood without close supervision. Not suitable for everyone, so discuss it with a qualified clinician or dietitian. |
| Lean gain, 300 kcal | TDEE + 300 | A conservative surplus for building muscle while keeping fat gain small. |
A fixed calorie deficit does not predict a fixed weekly weight loss. Water, stored carbohydrate, hormones and changes in how much you move all shift the scale, and the rate slows as your body adapts over the months.4
Calculator lower limits
The calculator never shows a target below 1,500 kcal for men or 1,200 kcal for women. These are software cutoffs, not proof that a target is safe, suitable or nutritionally complete, and your own needs can be higher. If a deficit would take you below them, the target is set to the limit and the result tells you. Discuss any lower intake with a qualified clinician or dietitian, particularly if you have a medical condition or take medication.
Starting targets PTD coaches use by goal
These are the ranges PTD Fitness coaches start from for three common goals among clients in Dubai and Abu Dhabi. Your coach then adjusts them against real measurements from your first few weeks.
| Goal | Calories | Protein per kg | Training at home | Typical change |
|---|---|---|---|---|
| Fat loss for men and women over 40 | TDEE − 450 to 600 kcal | 1.8–2.2 g | 3 full-body strength sessions a week, plus about 8,000 steps indoors or in the evening | About 0.5–0.8 kg of fat a week |
| On Mounjaro, Ozempic or another GLP-1 medicine | Agreed with your prescribing doctor; the bigger risk is usually eating too little | Upper end of 1.6–2.2 g, agreed with your doctor or dietitian | 2–3 strength sessions a week to protect muscle | Track waist, strength and body composition, not only the scale |
| Body recomposition: a smaller waist, more muscle | TDEE − 200 to 300 kcal | 2.0–2.2 g | 3–4 strength sessions a week at home, in a villa or in a building gym | Waist down 2–4 cm a month at a steady weight |
Individual results vary with starting point, attendance, sleep, health and consistency. Work out your own protein number with the protein calculator, and see the GLP-1 training guide if you take a weight-loss medicine.
Your coach sets your starting targets, then adjusts them against your measurements.
UAE context: heat, hydration and Ramadan
The calculator does not use a UAE-specific equation. Living here changes how much you move, when you eat and where you train, and these notes help you choose the right inputs.
Summer heat and your activity level
From June to September, Dubai and Abu Dhabi regularly pass 40°C, and outdoor exercise becomes impractical for most people. If you walk, run or cycle outside in the cooler months and stop or move indoors in summer, your real activity level falls. Choose the lower level in summer and move back up when the weather cools. Training at home with a PTD coach does not change with the season, because sessions happen in your air-conditioned home or building gym.
Hydration
Fluid needs vary with body size, exercise, weather and health. Keep water and a cool place to train close by. If a clinician has advised you to limit fluids, or you have symptoms that do not settle, follow their advice rather than a generic water target.
Ramadan
In Ramadan, meal timing, sleep and activity all change. Many people do better with a smaller deficit for the month, such as the 300 kcal option, and a training time when they can exercise comfortably and recover. The calculator does not apply a special Ramadan formula. If you take medication or have a health condition, discuss any changes with your clinician. The nutrition guide covers suhoor and iftar in detail.
What to do with your number
- Eat at your target for two to four weeks. Weigh yourself at the same time on a few mornings each week and watch the weekly average, not one day.
- Get enough protein. In a deficit, protein decides how much of the weight you lose is fat rather than muscle. The protein calculator gives your daily and per-meal target.
- Adjust by 100–200 kcal if your average has not moved after three weeks, or if you are losing much faster than planned.
- Lift weights two to four times a week. Strength training helps you keep muscle while the fat comes off, which matters even more after 40.
If you want someone to do this with you, a PTD coach builds your calorie and protein targets into a training plan at your home, building gym or office, and checks progress against measurements rather than the scale alone.
Free, at your place, with no obligation.
Sources
This calculator and guide are general education, not medical advice. The main references behind the numbers:
- Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition, 1990.
- Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. Journal of the American Dietetic Association, 2005.
- National Institute of Diabetes and Digestive and Kidney Diseases. Body Weight Planner. US National Institutes of Health.
- Hall KD. What is the required energy deficit per unit weight loss? International Journal of Obesity, 2008.
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