Our Calculator Methodology and Editorial Process

How we calculate TDEE and macros

The calculator starts by estimating basal metabolic rate, or BMR. BMR is the energy your body uses at rest before normal movement, exercise, digestion, and daily work are added. We implement three established equations: Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle. The default is Mifflin-St Jeor because it performs well in healthy adults using inputs most users can provide accurately: age, sex, height, and weight. The equation was published by Mifflin et al. in 1990 in the American Journal of Clinical Nutrition.

Harris-Benedict remains available because it is widely recognized and still appears in clinical and nutrition references. We use the 1984 Roza and Shizgal revision, not the original early twentieth century equation. The alternate formula gives users a comparison point, but it is not the default. Frankenfield, Roth-Yousey, and Compher reviewed predictive equations in healthy nonobese and obese adults and concluded that Mifflin-St Jeor was more likely than Harris-Benedict to estimate resting metabolic rate within 10% of measured values in healthy adults (Frankenfield et al. 2005).

Katch-McArdle is offered when the user provides body fat percentage. Unlike Mifflin-St Jeor and Harris-Benedict, it estimates resting energy expenditure from lean body mass. That can be useful for people whose body composition differs substantially from the average person at the same height and weight. Its accuracy depends on the body fat estimate. A rough visual estimate can make the output less reliable than a standard equation.

After estimating BMR, the calculator applies an activity multiplier to estimate total daily energy expenditure, or TDEE. The available multipliers run from 1.2 for little or no exercise through 1.9 for very hard training plus a physical job or twice-daily training. These factors are best estimates, not direct measurements. Real TDEE for one person often differs by 5 to 15% from formula predictions. The result should be treated as a starting calorie target, then adjusted against observed bodyweight change over 2 to 4 weeks.

Macro targets are calculated from the calorie target and the selected goal. Protein is anchored to bodyweight because resistance-trained people generally benefit from higher protein intakes during fat loss and muscle gain. Helms, Aragon, and Fitschen reviewed evidence for natural bodybuilders and cited a broad range of protein needs, including 1.6 to 2.2 g/kg for many resistance-trained people at or above maintenance, with higher needs possible in lean dieting phases (Helms et al. 2014). After protein is set, carbohydrate and fat are allocated from the remaining calories according to the selected diet preference.

Goal settings change calories before macros are split. A fat-loss goal applies a calorie deficit from estimated maintenance. A muscle-gain goal applies a surplus. A maintenance goal keeps the TDEE estimate unchanged and uses macros to organize intake around that calorie level. These goal adjustments are intentionally conservative because aggressive deficits and surpluses often create adherence problems and larger tracking error. The calculator gives a starting target that can be tested against real intake, training, appetite, and scale trend.

Why we default to Mifflin-St Jeor

Mifflin-St Jeor uses age, sex, height, and weight. Harris-Benedict uses the same ordinary inputs but applies a different equation. Katch-McArdle uses lean body mass, so it requires a body fat percentage before it can be calculated. The practical question for a public calculator is not which equation is perfect. None are. The question is which equation gives the best baseline for the largest number of users who know their height, weight, age, and sex but do not know their measured resting metabolic rate.

We default to Mifflin-St Jeor because Frankenfield, Roth-Yousey, and Compher compared common resting metabolic rate prediction equations in a systematic review published in the Journal of the American Dietetic Association. Their review found that Mifflin-St Jeor was more accurate than Harris-Benedict for healthy adults across a range of body compositions (Frankenfield et al. 2005). That finding matches the use case for this site: a general adult user looking for a reasonable starting estimate.

The trade-off matters. Even a good equation has meaningful individual error. A result that is close on average across a group can still miss one person by roughly 10%, sometimes more. A calculator output is a population estimate applied to an individual. It is the first number in a feedback loop, not a final verdict on metabolism.

We expose the alternate formulas because comparison is useful when the input quality changes. A user with a reliable body fat measurement may prefer Katch-McArdle. A user comparing results from another clinic, app, or coach may need Harris-Benedict for consistency. The default simply reflects the equation we consider most appropriate when ordinary user-entered inputs are all that is available.

Limitations of these formulas

Resting metabolic rate equations compress a complicated human body into a few variables. That makes them useful for fast estimates, but it also creates predictable blind spots. Mifflin-St Jeor and Harris-Benedict do not directly measure lean mass. A muscular person can burn more energy at rest than another person of the same height, weight, age, and sex because lean tissue is more metabolically active than fat tissue. In that case, a standard equation can underpredict needs.

The reverse can happen for some users with obesity. Excess fat mass contributes less to resting energy expenditure per unit than lean mass, so a bodyweight-based equation can overpredict needs when body fat is very high. Katch-McArdle can help when body fat percentage is known from a reliable method, but a poor body fat input creates its own error.

These formulas also do not account for thyroid status, medications that affect metabolism, recent weight loss, pregnancy, lactation, illness, or significant body composition asymmetry. Recent weight loss is especially relevant because energy expenditure often falls below what body size alone predicts. That adaptive drop is not captured by a standard BMR equation.

Users in any of these categories should treat the result as a rough starting point. The more reliable method is recalibration: track actual calorie intake, weigh consistently, and compare the bodyweight trend over 2 to 4 weeks. If weight is stable, average intake is close to real maintenance. If weight is changing, the rate of change gives a better estimate than any formula can provide by itself.

Recalibration works best when the inputs are boring and repeatable. Weigh under similar conditions, use a weekly average instead of one weigh-in, and compare intake only after unusually high-sodium meals, travel, illness, and hard training weeks have been considered. Short-term water changes can hide fat loss or create the appearance of weight gain. A 2 to 4 week trend is long enough to reduce that noise for most users.

What activity multipliers represent

Activity multipliers convert estimated BMR into estimated TDEE. They are meant to represent the combined effect of daily movement, formal exercise, physical work, and nonexercise activity. They are not a wearable-device replacement and they are not precise enough to distinguish every job, sport, or training schedule.

• 1.2: little or no exercise, desk job.
• 1.375: light exercise 1 to 3 days per week.
• 1.55: moderate exercise 3 to 5 days per week.
• 1.725: hard exercise 6 to 7 days per week.
• 1.9: very hard exercise plus a physical job, or twice-daily training.

Most people overestimate their activity level. A person who lifts weights three days per week but sits most of the day may be closer to lightly active than moderately active. A person who trains hard and also walks many miles at work may need a higher bracket. Choosing one bracket lower than your first instinct usually produces a more accurate baseline. Adjust upward only if you lose weight faster than expected at the calculated maintenance intake, or if training performance, hunger, and weight trend all point to underfueling.

Exercise calories are not added separately when an activity multiplier is used. The multiplier already includes expected training and daily movement. Adding workout calories on top of the calculated TDEE usually double-counts exercise unless a user is deliberately using a separate tracking system. For most people, the cleaner approach is to choose one multiplier, hold intake steady, and revise the target only after the bodyweight trend is clear.

Our editorial process

Our nutrition and fitness content starts with source review. We prioritize peer-reviewed studies, government dietary guidance, and position statements from professional bodies such as the Academy of Nutrition and Dietetics, the American College of Sports Medicine, ESPEN, and ACOG. We use secondary sources only when they help explain a topic or point readers toward the primary material.

Drafting may use AI tools as part of the workflow. AI output is not treated as a source, and it is not published without editorial review. Before publication, the SquarepegIdeas editorial team checks claims against the cited sources, removes claims that cannot be supported, and rewrites unclear guidance in plain language.

Calculator math is implemented from the original published formulas rather than copied from secondary tutorials. For each calculator, we verify unit conversions, expected input ranges, and common edge cases. If an equation is available only through a textbook source, we identify the source and avoid adding precision that the source does not support.

Each substantive page carries a last reviewed date. We review content at least every 12 months and sooner when a relevant formula, dietary guideline, professional position statement, or safety concern changes the accuracy of a page. When calculator math changes, we update the related methodology page within 30 days of that change.

Errors are corrected promptly when identified. Minor corrections, such as spelling or broken links, may be made without a note. Substantive corrections, including calculation errors, factual errors, or outdated guidance, are marked with a brief note on the affected page stating what changed and when.

We keep editorial review separate from product and advertising decisions. A page can recommend caution even when that caution lowers commercial value. A calculator can also remain free of product recommendations when the topic does not require them. This separation is especially important for nutrition content, where unsupported certainty can push readers toward changes that are not appropriate for their situation.

Sources we rely on

Our foundational calculator references include the Mifflin-St Jeor resting energy expenditure equation (Mifflin et al. 1990), the revised Harris-Benedict equations (Roza and Shizgal 1984), and the Katch-McArdle equation as presented in exercise physiology and nutrition texts. These sources define the math used for BMR estimates.

For formula selection and interpretation, we rely on comparative research such as Frankenfield, Roth-Yousey, and Compher's 2005 review of resting metabolic rate prediction equations. For macro targets and sports nutrition context, we use Helms, Aragon, and Fitschen's 2014 review for natural bodybuilders, Aragon and Schoenfeld's 2013 nutrient timing review, and Schoenfeld and colleagues' protein distribution research.

Population-specific guidance comes from professional bodies when available. ACOG guidance informs pregnancy and lactation cautions. ESPEN protein recommendations inform older-adult cautions. Government dietary guidance from agencies such as USDA, NIH, and FDA is used where it is the most direct source for public nutrition standards.

Questions about our methodology

We welcome specific feedback on formula implementation, source interpretation, and unclear explanations. The most useful reports include the page URL, the statement or calculation in question, and a primary source that supports the correction. Send methodology concerns through the Contact page.