Modeling daily energy expenditure from predicted resting expenditure
Total daily energy expenditure (TDEE) estimates the energy used across an ordinary day. This model first estimates resting expenditure from weight, height, age and one original-study equation constant, then applies a representative physical activity level. The output is in kilocalories, also called food Calories.
TDEE and resting energy expenditure answer different questions. Resting expenditure estimates the energy required while at rest; multiplying it by a physical activity level (PAL) produces a rough full-day expenditure estimate. A lifestyle factor includes ordinary movement at work and home as well as exercise. The example uses 70 kg, 175 cm and age 30 with the study's +5 constant: 700 + 1,093.75 − 150 + 5 = 1,648.75 kcal/day at rest. With PAL 1.55, modeled total is 2,555.5625 kcal/day. A food Calorie is a kilocalorie, so there is no additional conversion factor.
The visual separates a predicted resting baseline from the extra amount produced by the selected PAL, then shows how three sourced activity examples change the model. The estimate remains clearly labeled as expenditure, not a diet target.
How body measurements, age, equation constant and activity factor shape TDEE
The result combines a Mifflin–St Jeor resting prediction with an illustrative full-day activity multiplier. It does not prescribe food intake.
- Weight and height
- Enter kilograms and centimeters. The resting equation adds 10 kcal for each entered kilogram and 6.25 kcal for each entered centimeter before its age and source-equation adjustments.
- Age in whole years
- The form accepts 19–78, the original study's adult span. Each additional year subtracts 5 kcal/day from the predicted resting value when other inputs stay fixed.
- Original-study equation constant
- The published model uses +5 for its male equation or −161 for its female equation. These source categories do not represent every body or identity with equal precision.
- Illustrative lifestyle factor
- Choose a pattern for work, home and leisure across the day, not one workout. Multiplying the resting estimate by 1.55, 1.75 or 2.10 shows how sensitive the modeled total is to this choice.
Steps
- Enter adult weight in kilograms, height in centimeters and whole-year age within the supported study span.
- Choose the original Mifflin equation constant and the broad activity pattern closest to your usual full day.
- Read the resting estimate, chosen PAL and modeled total together; use the comparison as an illustration rather than a prescribed food intake.
Reading tip: Read the split between estimated rest and the modeled difference attributed to the activity multiplier. The three PAL rows reuse the same resting input; their spacing shows how sensitive the estimate is to the lifestyle selection.
Ways to compare a resting estimate with a full-day model
Learn the two energy terms
Compare predicted resting expenditure with a modeled full-day TDEE on the same inputs.
Check activity sensitivity
See how broad FAO lifestyle factors move the estimate without changing body inputs.
Read a food-Calorie unit
Interpret kcal/day and capital-C food Calories as the same energy unit.
Prepare a clinical question
Bring the stated assumptions and estimate to a qualified clinician when individual needs matter.
How the calculation works
- weight / height
- Entered kilograms / centimeters in the original resting-energy equation.
- age / C
- Whole years from 19 to 78 / chosen original-study sex-specific constant.
- REE
- Predicted resting energy expenditure in kilocalories per day, before activity adjustment.
- PAL
- Representative physical activity level multiplier for a habitual full-day lifestyle.
The result estimates expenditure in food Calories (kcal); it is not a prescribed intake, weight-change prediction or medical assessment.
What every part means
- weight / height
- Entered kilograms / centimeters in the original resting-energy equation.
- age / C
- Whole years from 19 to 78 / chosen original-study sex-specific constant.
- REE
- Predicted resting energy expenditure in kilocalories per day, before activity adjustment.
- PAL
- Representative physical activity level multiplier for a habitual full-day lifestyle.
Calculate it step by step
C is +5 for the study's male equation or −161 for its female equation; this is a predicted resting value, not a measurement.
PAL is the selected representative full-day activity factor, not the Calories from one workout.
This residual reflects the multiplier model. It is not a measured exercise calorie count.
The calculation retains unrounded decimal values through multiplication and rounds the large answer only for display. The available PAL examples are 1.55, 1.75 and 2.10, chosen within FAO/WHO/UNU adult lifestyle ranges 1.40–1.69, 1.70–1.99 and 2.00–2.40. The original resting equation was fitted on 498 adults aged 19–78; the form uses that age span rather than silently extrapolating to children.
See how Calculation Guide tests examples and handles calculation limits.
See it in practice
- Body weight
- 70 kg
- Height
- 175 cm
- Age
- 30 whole years, 19–78
- Original-study equation constant
- Male equation: +5
- Illustrative lifestyle factor
- Sedentary/light · PAL 1.55
At 70 kg, 175 cm, age 30, C=+5: REE = 700+1,093.75−150+5 = 1,648.75 kcal/day. At PAL 1.55, TDEE = 1,648.75×1.55 = 2,555.5625, shown as about 2,556 kcal/day.
- Estimated resting expenditure1,648.75 kcal/day
- Chosen activity multiplier1.55
Interpretation & limitations
How to read your result
In the worked example, the resting estimate is 1,648.75 kcal/day and the modeled full-day expenditure is about 2,556 kcal/day at PAL 1.55. Selecting PAL 1.75 changes the illustration to 2,885.31 kcal/day without changing weight, height or age. This difference is model sensitivity; it does not prove that a person's actual energy use changed by that amount.
Where this estimate stops
FAO defines PAL against basal metabolic rate, while the Mifflin equation predicts resting energy expenditure; applying a PAL to that prediction is a rough practical approximation. This static estimate cannot model changing body mass, adaptive metabolism, exact activity duration or individual body composition. The original equation has two sex-specific constants and may not fit everyone. Pregnancy, breastfeeding, illness and special clinical or athletic circumstances can alter energy needs. The page does not calculate a weight-loss deficit or prescribe food intake; for individualized decisions, use clinical guidance and a more detailed tool such as NIDDK's Body Weight Planner.
Frequently asked questions
01Is a food Calorie the same as a kilocalorie?
Yes. In nutrition labeling, one capital-C Calorie is one kilocalorie (kcal). The result uses those units per day.
02Does this tell me exactly how many Calories to eat?
No. It estimates expenditure using a prediction equation and a broad activity factor. Individual dietary needs and health conditions require more context.
03Is resting energy expenditure the same as TDEE?
No. REE is the prediction before the activity factor; TDEE applies a PAL to represent a whole day's expenditure.
04Which activity factor should I choose?
Choose the broad pattern of your usual work, travel and leisure. The three factors are examples inside population ranges, so compare outputs if your routine lies near a boundary.
05Why are there only two equation constants?
The original Mifflin study fitted separate male and female equations. This limitation is shown so the calculator does not claim to describe every body or identity precisely.
06Is the resting number BMR?
No. Mifflin–St Jeor predicts resting energy expenditure (REE), while a measured basal metabolic rate (BMR) has stricter measurement conditions. This page labels the calculated number REE and does not claim a measured BMR.