TDEE, BMR & PAL — how many calories you actually need

Three calorie calculators, three results, all different — and none of them tells you why. Behind it sits the math of BMR (basal metabolic rate), PAL (activity factor), and TDEE (total daily energy expenditure), plus three competing formulas built on different assumptions. This article explains what they do, which one to use, and why the final number is just a starting point.

BMR — what your body burns at rest

Basal Metabolic Rate (BMR) is the energy your body needs just for upkeep: heartbeat, breathing, body temperature, brain activity, cell renewal. It's classically measured after 12 hours of fasting, lying at rest, at 20 °C. For an adult woman it typically sits at 1,300 to 1,500 kcal, for an adult man at 1,600 to 1,900 kcal per day.

Important: BMR is highly individual. Muscle mass increases it, diets reduce it (adaptive thermogenesis), hormonal status, genetics, and climate all play a role. Every formula gives a statistical estimate — a real measurement would require a metabolic chamber (indirect calorimetry).

The three main BMR formulas

Three formulas dominate practice. They differ mainly in their data basis and whether they account for body fat:

• Harris-Benedict (1919, revised 1984): the historical reference, based on measurements of about 250 people in the early 20th century. Tends slightly too high for modern lifestyles (more overweight, less muscle mass).
• Mifflin-St Jeor (1990): developed on a larger, more contemporary sample and is today's gold standard in sports and nutrition science for adults without a body fat measurement.
• Katch-McArdle: requires body fat percentage as input and calculates against lean body mass. More accurate for athletic or very overweight individuals, because metabolic activity comes almost exclusively from lean body mass.

PAL — the activity factor turns BMR into TDEE

TDEE (Total Daily Energy Expenditure) is BMR times PAL (Physical Activity Level). The PAL is a multiplier that represents average physical activity. The WHO and equivalent national agencies typically use these levels:

• 1.2 to 1.25: bedridden, almost entirely sedentary (e.g. post-surgery).
• 1.4 to 1.5: mostly sedentary work with little movement in free time (office job, work-from-home without sport).
• 1.6 to 1.7: sedentary work, but partly standing or walking (teachers, sales staff, lots of housework).
• 1.8 to 1.9: mostly standing or walking work (trades, nursing, service hospitality).
• 2.0 to 2.4: heavy physical work or several hours of intense training per day (construction, pro athletes).

TEF and NEAT — the underrated factors

The Thermic Effect of Food (TEF) is the energy your body spends digesting, metabolizing, and storing food itself. Roughly 10 percent of intake is the rule of thumb — but protein costs up to 30 percent, carbohydrates 5 to 10 percent, fat only 0 to 3 percent. A protein-heavy diet therefore burns measurably more than a fat-heavy one at the same calorie count.

NEAT (Non-Exercise Activity Thermogenesis) is all the movement you do outside of dedicated exercise: gesturing, tapping your foot, getting up, taking stairs. NEAT studies show differences of up to 2,000 kcal per day between seemingly identical people — more than any normal training session. To lose weight, take NEAT just as seriously as the workout.

From TDEE to a calorie goal

Once you have your TDEE, most goals come down to a simple adjustment:

• Lose weight: TDEE minus 300 to 500 kcal per day — yields roughly 0.3 to 0.5 kg of fat loss per week. Larger deficits are possible short-term but psychologically and hormonally harder to sustain.
• Maintain: hit your TDEE precisely. Sounds simple, isn't — a 100 kcal daily surplus means 4 to 5 kg of weight gain per year.
• Gain: TDEE plus 200 to 400 kcal per day (lean bulk). More surplus means more fat, not more muscle — muscle gain is physiologically capped.

Why the calculator value is only a starting point

Studies show that even the best BMR formula can be off by ±200 kcal in individual cases — and inaccurate PAL estimates can add another ±300 kcal of error. Anyone who doesn't lose weight in two weeks despite a planned deficit doesn't have a 'broken metabolism' — their real TDEE is likely 300 kcal below the calculator value.

The honest method: track consistently for 7 to 14 days (weighing, logging, steps), then adjust the planned surplus or deficit based on real weight change. 7,700 kcal equals roughly 1 kg of fat — anyone who lost 0.5 kg in a week had a deficit of about 550 kcal per day, regardless of what the calculator said up front.

Frequently asked questions

Which formula should I use if I have no measurements?

Mifflin-St Jeor. It performs best in comparison studies (e.g. ADA 2005) and only needs sex, age, height, and weight. Harris-Benedict is historically interesting but averages 5 to 7 percent too high. Katch-McArdle only if you have a reliable body fat measurement — otherwise you stack two layers of estimation error.

Are 1,200 kcal safe for weight loss?

It's an internet myth number. 1,200 kcal is below BMR for many women — not sustainable and hormonally problematic in the medium term (cycle disruption, thyroid, bone density). A realistic minimum for adults with normal activity is closer to BMR + 100 kcal. When in doubt, see a nutritionist instead of following an online rule of thumb.

Should I include workouts in PAL or add them as extras?

Both work if you stay consistent. Option A: PAL captures baseline activity (e.g. 1.4 for an office job), workouts get added per day. Option B: PAL includes average sport (e.g. 1.55 for 3 workouts per week), nothing is added on top. Mixing both leads to double-counting and broken math — pick one method.