How to Calculate Macros for Weight Loss: TDEE, Deficit & Protein Floor

There are four numbers worth calculating and one mistake to avoid. The numbers: (1) BMR via the Mifflin-St Jeor 1990 equation^[1]; (2) TDEE via the FAO/WHO 2001 activity multiplier on top of BMR; (3) a 250–500 kcal/day deficit per the Hall 2011 Lancet dynamic-energy-balance model^[2]; (4) a protein floor first — 1.6 g/kg/day per the Morton 2018 meta-analysis of 49 RCTs^[3] (the plateau dose for muscle gain on resistance training), bumped to 1.8–2.2 g/kg on a GLP-1 per the Neeland 2024 review^[7]. Fat takes 0.4–0.5 g/kg as a hormonal floor; carbs absorb the remainder. The mistake to avoid: thinking macros are the intervention. STEP-1 semaglutide^[8] produced −14.9% body weight at 68 weeks and SURMOUNT-1 tirzepatide^[9] produced −20.9% at 72 weeks — pharmacology drove the appetite suppression. Macros are how you preserve lean mass and stay inside the deficit, not how you get to the deficit.

TL;DR

• Step 1 — BMR (Mifflin-St Jeor 1990^[1]). Men: 10 × kg + 6.25 × cm − 5 × age + 5. Women: 10 × kg + 6.25 × cm − 5 × age − 161.
• Step 2 — TDEE. Multiply BMR by your activity factor: sedentary 1.2, light 1.375, moderate 1.55, very active 1.725, extreme 1.9 (FAO/WHO/UNU 2001 PAL values).
• Step 3 — Deficit. Subtract 250–500 kcal/day from TDEE. Hall 2011 Lancet^[2] showed the classic “3,500 kcal = 1 lb” rule systematically overpredicts loss because metabolic adaptation slows the rate at lower body weights.
• Step 4 — Protein floor first. Target 1.6 g/kg body weight (Morton 2018^[3], plateau of additional muscle-mass gain on resistance training); 1.8 g/kg on a GLP-1 (Neeland 2024^[7]); 2.2 g/kg if you are also resistance-training in a 25%+ deficit (ISSN 2017 upper-bound^[4]).
• Step 5 — Fat + carbs. Fat at 0.4–0.5 g/kg minimum (hormonal floor); carbs absorb the leftover calories. Distribute protein across 3–4 meals at ~0.3–0.4 g/kg per meal (Mamerow 2014^[5]).
• Magnitude reality check. Even a perfect macro split inside a 500 kcal/day deficit gets you about 0.45 kg/week loss^[2]. STEP-1 semaglutide^[8] produced −14.9% body weight at 68 weeks; SURMOUNT-1 tirzepatide^[9] produced −20.9% at 72 weeks. Macros do not put you in that magnitude range. Macros decide how much of the loss is fat versus lean tissue.

Step 1 — Calculate BMR with the Mifflin-St Jeor equation

Basal metabolic rate is the energy your body uses at rest — breathing, circulation, brain activity, thermogenesis. It is the floor of your daily energy expenditure. The Mifflin-St Jeor 1990 equation^[1] is the current gold standard for predicting BMR from weight, height, age, and sex; it was validated against indirect calorimetry in n=498 adults (247 women, 251 men), ages 19–78, spanning normal-weight to obese BMI ranges, and is more accurate than the older Harris-Benedict 1919 and Schofield 1985 equations in modern populations.

The formula

• Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5
• Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) − 161

Worked example

A 35-year-old male, 200 lb (90.7 kg), 5′10″ (178 cm):

• 10 × 90.7 = 907
• 6.25 × 178 = 1,112.5
• 5 × 35 = 175
• 907 + 1,112.5 − 175 + 5 = 1,850 kcal/day BMR

A 35-year-old female, 170 lb (77.1 kg), 5′5″ (165 cm):

• 10 × 77.1 = 771
• 6.25 × 165 = 1,031.3
• 5 × 35 = 175
• 771 + 1,031.3 − 175 − 161 = 1,466 kcal/day BMR

Step 2 — Multiply BMR by activity factor to get TDEE

Total daily energy expenditure (TDEE) is BMR plus the thermic effect of food plus all your physical activity. FAO/WHO/UNU 2001 Human Energy Requirements published standard Physical Activity Level (PAL) multipliers that are used in nutrition planning worldwide:

For the 200-lb male above at light activity: 1,850 × 1.375 =~2,544 kcal/day TDEE. For the 170-lb female at light activity: 1,466 × 1.375 = ~2,016 kcal/day TDEE.

Most people overestimate their activity level. If you have a desk job and lift weights three times a week, you are “light,” not “moderate.” If your weight is stable, your current intake is your TDEE — that empirical estimate trumps any formula. Track for 7–14 days at maintenance before applying a deficit.

Step 3 — Subtract 250-500 kcal/day for the deficit

The classic textbook rule says 3,500 kcal = 1 lb of fat, so a 500 kcal/day deficit yields ~1 lb/week loss. The Hall 2011 Lancet paper^[2] showed this static model systematically overpredicts loss in the real world because metabolic adaptation (adaptive thermogenesis + lower body-mass-driven BMR + reduced spontaneous activity) slows the rate as you lose weight. The dynamic-energy-balance model in Hall 2011 estimates closer to ~10 lb/year lost per 100 kcal/day sustained deficit over a long time horizon — not the optimistic ~10 lb every 70 days the static rule predicts.

Practical deficit tiers:

• Conservative — 250 kcal/day deficit. ~0.5 lb/week initial rate. Best for body recomposition, people close to goal weight, and patients prioritizing lean-mass preservation.
• Moderate — 500 kcal/day deficit. ~1 lb/week initial rate. The standard textbook recommendation. Sustainable for most adults with a starting BMI above 30.
• Aggressive — 750–1,000 kcal/day deficit. ~1.5–2 lb/week. Accelerates lean-mass loss without accelerating fat loss proportionally; Cava 2017^[6] reviews the evidence that the LBM share of total weight loss rises as the deficit deepens. Reserve for short bursts under clinical supervision, never below ~1,200 kcal/day for women or ~1,500 for men.

For the 200-lb male at TDEE 2,544: a 500 kcal deficit lands at ~2,044 kcal/day target intake. For the 170-lb female at TDEE 2,016: a 500 kcal deficit lands at~1,516 kcal/day (below the 500 mark would push under the 1,200 floor, where micronutrient deficits and adaptive thermogenesis penalties dominate).

Step 4 — Protein floor first

The most important macro number for weight loss is protein, and the right floor depends on whether you are resistance-training and whether you are on a GLP-1.

The Morton 2018 Br J Sports Med systematic review and meta-analysis^[3] pooled 49 randomized controlled trials (n=1,863 adults). The meta-regression found that protein supplementation increased fat-free mass and lean strength gains on resistance training in a dose-dependent way until a plateau at ~1.62 g/kg/day of total protein intake; beyond that point, additional protein did not produce additional muscle. The ISSN 2017 Position Stand on protein and exercise^[4] recommends 1.4–2.0 g/kg/day for most exercising individuals, rising to 2.3–3.1 g/kg of lean body mass during sustained energy restriction in very lean populations (contest prep, severe cut).

For patients on a GLP-1 receptor agonist, the Neeland 2024 Diabetes Obes Metab review^[7] documents that DXA-substudy data from STEP and SURMOUNT trials show roughly 25–39% of weight lost on semaglutide and tirzepatide comes from lean tissue without intervention. Neeland recommends 1.6–2.3 g/kg of fat-free mass; in practice, this maps to 1.8–2.2 g/kg of body weight for most patients. Cava 2017^[6] independently concluded that 1.6 g/kg/day is the practical floor for preserving healthy muscle during weight loss.

Protein-target table by body weight

Distribute protein across 3–4 meals at ~0.3–0.4 g/kg per meal. Mamerow 2014^[5] showed even distribution (~30 g x 3 meals) increased 24-hour muscle protein synthesis by ~25% versus skewed distribution (skipping breakfast, all-in at dinner) at the same total intake. Three meals of ~50 g for a 200-lb adult, or four meals of ~40 g, both work.

Step 5 — Fat at 0.4-0.5 g/kg, carbs absorb the rest

Once protein is locked in, fat should hit a hormonal floor of ~0.4–0.5 g/kg/day. Below that, sex hormones and fat-soluble vitamin absorption can be impaired in sustained restriction. There is no upper-bound “fat is fattening” rule that survives RCT data — calorie balance dominates. Higher-fat-lower-carb (Mediterranean, low-carb) and lower-fat-higher-carb diets produce equivalent weight loss when calories and protein are matched.

The math, continuing the 200-lb male example:

• Target intake: 2,044 kcal/day
• Protein: 163 g (GLP-1 target) × 4 kcal/g = 652 kcal
• Fat: 0.5 g/kg × 91 kg = 46 g × 9 kcal/g = 414 kcal
• Remaining for carbs: 2,044 − 652 − 414 = 978 kcal → 978 / 4 = ~244 g carbs

Fat can go higher (and carbs lower) if you prefer that eating pattern. The floor is what matters; the split above the floor is preference. Distribute fat across meals naturally; do not chase a specific fat-per-meal target.

How GLP-1s change the macro math

GLP-1 receptor agonists (semaglutide / Wegovy / Ozempic, tirzepatide / Zepbound / Mounjaro) change three things about macro calculation, none of them well-understood by most macro calculators online.

1. The deficit is appetite-driven, not counted. STEP-1^[8] and SURMOUNT-1^[9] participants did not count calories — appetite suppression dropped their intake into the deficit zone automatically. Most GLP-1 patients are eating 500–1,000 kcal/day below their pre-drug intake without trying. The macro math becomes a verification exercise (am I eating enough to preserve lean mass?), not a programming exercise (how do I create a deficit?).
2. Hitting the protein floor is harder, not easier. Appetite suppression is non-selective — patients do not crave protein more than carbs, they just want less of everything. Cava 2017^[6] and Neeland 2024^[7] both note that GLP-1 patients tend to drift well below 1.0 g/kg without realizing it because satiety hits before they finish a high-protein meal. The fix is protein-first eating (see our what to eat on a GLP-1 diet protein guide) and liquid protein (shakes) when solid food is hard. The GLP-1 Protein & Macro Calculator implements the entire 4-step formula above and bumps the protein tier automatically when you flag GLP-1 use.
3. Lean-mass loss is the real risk, not stalling. Neeland 2024^[7] reviewed the STEP / SURMOUNT body-composition substudies and reported 25–39% of total weight lost on these drugs is lean tissue without intervention — see our semaglutide and muscle mass deep-dive for the full DXA breakdown. The macros question on a GLP-1 is “how do I keep muscle?” not “how do I lose weight?” The answer is the 1.8–2.2 g/kg protein floor plus 2–3 resistance-training sessions per week.

Common bad takes

“Count every gram or it does not work”

Counting every gram is a tool, not a religion. The Hall 2011 dynamic model^[2] shows that even precise calorie counting drifts from the predicted weight-loss curve because adaptive thermogenesis is real. For most adults, the sustainable practice is: hit your protein target every day, weigh yourself weekly, and adjust intake by ~150 kcal/day if the trend stalls for 2+ weeks. Daily gram-level precision is necessary for contest prep and unnecessary for general fat loss.

“Low carb is magic”

It is not. Multiple meta-analyses comparing isocaloric low-carb versus low-fat diets show equivalent long-term weight loss when protein is matched. Low-carb works for some people because protein-and-fat-dominant meals are satiating, which makes the deficit easier to sustain. That is a behavioral mechanism, not a metabolic one. If you prefer carbs, eat them — calorie balance dominates.

“If it fits your macros (IIFYM)”

IIFYM is a body-recomposition framework popular in bodybuilding subculture: track protein, fat, and carbs to a gram and any food source counts as long as it fits. It is a useful intermediate tool for trained lifters in maintenance or recomp. It is not weight-loss advice for general adults, because it ignores fiber, micronutrient density, and satiety differences between food sources. A 2,000 kcal day of Pop-Tarts is technically IIFYM-compatible and will produce worse hunger, worse adherence, and worse body composition than 2,000 kcal of cottage cheese, salmon, oats, and berries at the same macro split.

“The protein RDA (0.8 g/kg) is enough”

The 0.8 g/kg/day RDA is the minimum to prevent deficiency in sedentary adults, not the optimum for fat loss with lean-mass preservation. Cava 2017^[6], Morton 2018^[3], the ISSN 2017 Position Stand^[4], and Neeland 2024^[7] all converge on 1.6–2.2 g/kg for active adults and patients losing weight, with the upper end of the range reserved for GLP-1 users and aggressive cuts.

Practical use

• Use the calculator, not the spreadsheet. The GLP-1 Protein & Macro Calculator on this site runs the full Mifflin-St Jeor + FAO/WHO PAL + Hall 2011 deficit + Morton 2018 protein-tier logic in a single form. Toggle the “on GLP-1” switch and it bumps the protein tier per Neeland 2024.
• Track protein, not everything. Track protein-rich foods daily; let calories find their natural floor under GLP-1 appetite suppression. If weight is not moving after 4 weeks at the calculated target, then add ~150 kcal/day to the cut.
• Distribute across 3–4 meals. ~0.3–0.4 g/kg per meal hits the leucine threshold for muscle protein synthesis each time (Mamerow 2014^[5]). A 200-lb adult: ~50 g protein x 3 meals.
• Reassess at 5% weight loss. BMR drops as you lose weight; re-run the calculation every time you have lost 5% of body weight to keep the deficit honest.
• Resistance-train, do not just cardio. See our semaglutide muscle mass guide for the protocol. 2–3 sessions per week of compound lifts is the published minimum dose for preserving lean mass in a deficit (Cava 2017^[6]).
• Use whole-food protein anchors. A 100 g serving of cooked salmon delivers ~22 g protein at ~206 kcal; a 1-cup serving of lowfat cottage cheese delivers ~25 g casein at ~163 kcal. Two of those a day covers 47 g of high-quality protein in 369 kcal.

Bottom line

Calculate four numbers in order: BMR (Mifflin-St Jeor 1990^[1]), TDEE (BMR x activity factor), target intake (TDEE − 250–500 kcal/day per Hall 2011^[2]), protein floor (1.6 g/kg/day per Morton 2018^[3]; 1.8–2.2 g/kg on a GLP-1 per Neeland 2024^[7]). Fat takes 0.4–0.5 g/kg as a hormonal floor; carbs absorb whatever calories are left. Distribute protein across 3–4 meals to maximize 24-hour muscle protein synthesis (Mamerow 2014^[5]).

Two reality checks. One: the macro split is not the intervention. STEP-1 semaglutide^[8] produced −14.9% body weight in 68 weeks and SURMOUNT-1 tirzepatide^[9] produced −20.9% in 72 weeks — pharmacology drove the deficit. Macros decide how much of the loss is fat versus lean tissue (Cava 2017^[6], Neeland 2024^[7]), not whether loss happens. Two: on a GLP-1, the macro problem flips. Hitting the protein floor on a suppressed appetite is harder than counting carbs, and lean-mass loss is the real risk (25–39% of total weight lost in STEP / SURMOUNT DXA substudies without intervention^[7]). The macro calculation matters more on a GLP-1, not less.

For the calculator that runs all of this in one form, see the GLP-1 Protein & Macro Calculator. For protein-source rankings and per-meal templates, see our what to eat on a GLP-1 diet protein guide. For the lean-mass-preservation protocol with exact resistance-training programming, see our semaglutide and muscle mass deep-dive. For the two highest-leverage whole-food protein anchors, see our salmon for weight loss evidence review and cottage cheese for weight loss evidence review.

Spanish edition forthcoming at /es/research/como-calcular-macros-perdida-peso-guia.