How to Calculate Maintenance Calories (TDEE, Done Right)
Your maintenance calories are the number you can eat each day without gaining or losing weight, and the cleanest way to estimate them is Mifflin-St Jeor for basal metabolic rate multiplied by an activity factor between 1.2 and 1.9. For an 80 kg, 35-year-old, 178 cm tall man at a sedentary desk job, that math lands near 2,460 kcal per day. For an equally average 65 kg, 35-year-old, 165 cm woman at the same activity level, near 1,825 kcal. Both numbers are starting estimates. The actual maintenance number sits inside a 200 to 400 kcal window around the estimate, and you do not know which side of the window you live on until you eat the estimate consistently for two to three weeks and watch what the scale does.
TL;DR
- Maintenance calories = BMR x activity multiplier (1.2 sedentary to 1.9 elite athlete). For most desk workers who do 3 to 4 workouts per week, 1.55 lands close.
- Mifflin-St Jeor is the default BMR equation. The Frankenfield 2005 systematic review called it the most reliable predictor of resting metabolic rate, within 10% of measured RMR.
- Katch-McArdle is more accurate if you know your body fat percentage (DEXA, BodPod). It scales BMR off lean body mass directly.
- Activity multipliers are the noisy variable. Most people who pick "moderately active" are actually sedentary plus three workouts, closer to 1.4 to 1.5, not 1.55 to 1.7.
- NEAT can swing daily energy expenditure by 800 to 1000 kcal between a sedentary day and a heavily active day, per Levine's 2002 review.
- Metabolic adaptation is real. The Muller 2015 reanalysis measured adaptive thermogenesis at roughly 48% of the REE decline during severe restriction.
- Real maintenance number = the calorie intake that holds your 7-day weight average stable for 3 weeks straight.
Want the math done for you?
The FitFixLife Calorie Calculator runs Mifflin-St Jeor (and Katch-McArdle if you supply body fat) with your activity multiplier.
Use the Free Calorie CalculatorWhy trust this guide
I am Kazi Habib, B.Pharm, MBA, PMP. The formulas, multipliers, and physiology below come from the peer-reviewed energy-expenditure literature on PubMed (Mifflin 1990, Frankenfield 2005, Knab 2011, Levine 2002, Muller 2015, Stiegler 2006, Tinsley 2019, Westerterp-Plantenga 2004), the NIH Office of Dietary Supplements energy requirement tables, and Health Canada Dietary Reference Intakes.
What maintenance calories actually means
The four components of total daily energy expenditure (TDEE):
- BMR (basal metabolic rate). 60 to 70% of TDEE for sedentary adults.
- TEF (thermic effect of food). Protein 20 to 30%, carbs 5 to 10%, fat 0 to 3%. Averages ~10% of intake.
- EAT (exercise activity thermogenesis). Structured exercise. 5 to 15% of TDEE for non-athletes.
- NEAT (non-exercise activity thermogenesis). Everything else. The most variable and most underappreciated. NEAT swings of 800 to 1000 kcal per day are documented.
The two prediction equations worth knowing
Mifflin-St Jeor (the default)
The Mifflin et al. 1990 paper developed prediction equations from 498 healthy adults:
- Men: REE (kcal/day) = (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) + 5
- Women: REE (kcal/day) = (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) - 161
Worked example, 80 kg, 178 cm, 35-year-old man: REE = (10 x 80) + (6.25 x 178) - (5 x 35) + 5 = 800 + 1,112.5 - 175 + 5 = 1,742.5 kcal/day.
Katch-McArdle (the body-composition upgrade)
RMR (kcal/day) = 370 + (21.6 x lean body mass in kg)
Lean body mass = total body weight - (body fat percentage x total body weight). The catch is that the input is only as accurate as your body fat measurement. DEXA scans are the practical gold standard ($75 to $150 in most Canadian cities).
Worked example, 80 kg man at 15% body fat: Lean body mass = 80 - (0.15 x 80) = 68 kg. RMR = 370 + (21.6 x 68) = 1,838.8 kcal/day. That is ~96 kcal higher than the Mifflin estimate for the same person.
Activity multipliers: the part most people get wrong
| Multiplier | Label | Real-life meaning |
|---|---|---|
| 1.2 | Sedentary | Desk job, almost no walking, no structured exercise |
| 1.375 | Light | Desk job + 1 to 3 light workouts per week |
| 1.55 | Moderate | Desk job + 3 to 5 moderate workouts per week |
| 1.725 | Active | Physical job OR 6 to 7 hard workouts per week |
| 1.9 | Very active | Physical job AND daily hard training |
The most common mistake: picking moderately active when lightly active is the truth. A 9-to-5 desk worker who lifts weights for 60 minutes three times per week is at roughly 1.4 to 1.5 in real terms, not 1.55. Picking 1.55 inflates the daily estimate by 100 to 200 kcal.
A more honest activity-multiplier calibration
| Real week pattern | Better multiplier |
|---|---|
| Desk job, under 5,000 steps daily, no structured workouts | 1.2 |
| Desk job, 5,000 to 8,000 steps, 1 to 2 short workouts per week | 1.3 to 1.35 |
| Desk job, 8,000 to 10,000 steps, 3 to 4 moderate workouts | 1.4 to 1.5 |
| Desk job, 10,000+ steps, 4 to 6 moderate workouts | 1.5 to 1.6 |
| Mixed standing/walking job + 3 to 5 moderate workouts | 1.6 to 1.7 |
| Physical labor + structured training | 1.7 to 1.85 |
| Elite athlete in heavy training block | 1.85 to 2.1 |
The adjustment loop: turning the estimate into the real number
- Eat the estimated maintenance number consistently for 14 to 21 days. Daily intake within +/- 100 kcal of the estimate.
- Weigh yourself every morning, same conditions. Track the 7-day rolling average. Daily weight swings of 1 to 2 kg are normal.
- At day 14 to 21, compare the 7-day average to the starting 7-day average:
- Stable within +/- 0.3 kg: estimate is the maintenance number.
- Down 0.4 to 1.0 kg: add 100 to 200 kcal/day, re-test.
- Up 0.4 to 1.0 kg: subtract 100 to 200 kcal/day, re-test.
- Changed by more than 1.0 kg: recheck both the multiplier and the food log.
- Re-run the loop whenever your training or schedule changes meaningfully.
Metabolic adaptation
The Muller et al. 2015 reanalysis of the Minnesota Starvation Experiment measured adaptive thermogenesis at roughly 48% of the decrease in resting energy expenditure during severe restriction. Practical implications: a 20% deficit producing 1% bodyweight loss per week is the safe range for most adults. Maintenance calories at a 10 kg lighter bodyweight are usually 200 to 400 kcal lower than the original maintenance. Re-run the adjustment loop after every 5 to 10 kg of change.
Pharmacist note: medications that change the math
- Thyroid medication (levothyroxine). Once at therapeutic TSH, BMR normalizes within weeks.
- Beta-blockers. Heart-rate-based calorie burn estimates become useless. Use perceived exertion (RPE 6 to 8) instead.
- SSRIs and SNRIs. Paroxetine and mirtazapine in particular are associated with weight gain partially independent of dietary intake.
- Antipsychotics (olanzapine, risperidone, clozapine, quetiapine). Maintenance estimates are often 200 to 400 kcal too high in patients on these medications.
- Corticosteroids. Increase appetite, cause fluid retention, shift body composition toward central fat.
- GLP-1 agonists (semaglutide, liraglutide, tirzepatide). Suppress appetite; calorie-math impact is mostly via reduced intake rather than altered TDEE.
- Pregnancy. Maintenance calories rise by roughly 340 kcal/day in the second trimester and 450 kcal/day in the third.
- Breastfeeding. Adds roughly 450 to 500 kcal/day of energy demand for exclusive breastfeeding in the first 6 months.
Common calculation mistakes
- Picking too high an activity multiplier.
- Under-reporting food intake. People under-report by 20 to 40% on food logs, even when motivated.
- Over-estimating exercise calorie burn. A 60-minute weightlifting session burns 250 to 400 kcal, not 600 to 800.
- Mixing equations between calculators. Starting estimates can vary by 200 to 300 kcal across tools.
- Treating the starting estimate as the final answer. Skipping the adjustment loop is the difference between a number that works and one that feels right.
- Not re-calibrating after significant body composition change.
- Eating off-diet on weekends and assuming weekday accuracy carries the average. The 7-day average is the number that matters.
Bottom line
Mifflin-St Jeor BMR x an honestly calibrated activity multiplier (1.2 to 1.9) gives you a starting maintenance-calorie estimate. Katch-McArdle is a slight upgrade if you have a reliable body fat percentage. The estimate is accurate within roughly +/- 200 to 400 kcal. The real maintenance number is what holds your 7-day weight average stable over 14 to 21 days of consistent eating. The biggest source of error is picking too high an activity multiplier; most people who pick "moderately active" should be at 1.4 to 1.5, not 1.55.
If you want the math done for you, the FitFixLife Calorie Calculator runs Mifflin-St Jeor (and Katch-McArdle if you supply body fat) with your activity multiplier. Pair it with the FitFixLife Macro Calculator to break the daily calorie target into protein, carb, and fat allocations.
Frequently Asked Questions
For most adults: Mifflin-St Jeor for BMR, applied with an honestly calibrated activity multiplier (1.2 to 1.9), with the result confirmed by a 14 to 21 day adjustment loop comparing 7-day weight averages. For muscular adults who know their body fat percentage, Katch-McArdle slightly outperforms Mifflin because it scales off lean body mass directly.
Three usual reasons: the activity multiplier you picked was higher than your real activity (most common), your food log is under-reporting by 15 to 25% (also common), or your body has adapted by lowering NEAT and slightly lowering RMR (real and well-documented in deficits over 4+ weeks). Run the 14 to 21 day adjustment loop with weighed food and a 7-day moving average.
For trend tracking (am I more active this week than last week), yes. For absolute daily calorie targeting, treat the number as accurate within +/- 20 to 25%. Heart-rate-based estimates are particularly imprecise for resistance training, and EPOC effects after vigorous exercise are not captured cleanly by any consumer wearable.
After every 5 to 10 kg of weight change, after a meaningful change in training volume, after a new job or schedule change, after a medication start or stop, and after a season change. Otherwise once per year is enough for stable adults at stable bodyweight.
Yes. The simpler approach for fat loss is to start at the Mifflin estimate minus 500 kcal per day, track 7-day weight average, and adjust by 100 to 200 kcal per day every two weeks based on the actual trend. You do not strictly need the precise maintenance number to lose weight; you need to be in a deficit that produces 0.5 to 1% bodyweight loss per week.
Marginally. Six small meals per day vs three large meals per day does not change total daily energy expenditure meaningfully. Intermittent fasting protocols do not change maintenance through any metabolic boost mechanism (that claim is not supported by trial evidence), but they often help people eat less by compressing the eating window. Net calories are what move the scale.
The Harris-Benedict equations were derived in 1919 from a small sample and overestimate measured REE by roughly 5% on average versus Mifflin. The revised 1984 Harris-Benedict equations are closer but still less accurate than Mifflin-St Jeor in modern populations. Use Mifflin.
Close but not identical. BMR is measured after an overnight fast in a thermoneutral lab. RMR is the practical version measured under less strict conditions and is usually 5 to 10% higher than true BMR. The prediction equations estimate values close enough to either that the distinction is mostly academic for everyday maintenance-calorie use.
Each kg of muscle burns roughly 13 kcal per day at rest. Each kg of fat burns roughly 4.5 kcal per day at rest. The often-repeated claim that adding 1 kg of muscle adds 50 to 100 kcal per day to BMR is overstated; the real number is closer to 10 to 15 kcal per day per kg of muscle at rest.
Daytime fasting compresses the eating window without changing total daily energy needs meaningfully for most adults; the maintenance number still applies, just split across a smaller window. Extended fasting (24+ hours) reduces BMR slightly through metabolic adaptation.
Kazi Habib
B.Pharm · MBA · PMP · Digital Marketing, York University
Kazi Habib is the founder of FitFixLife. With over 10 years in pharmaceutical and life sciences marketing, a Digital Marketing certification from York University (Toronto), and hands-on experience launching nutraceutical products at Beximco Pharmaceuticals — including science-backed meal replacers for weight management and diabetic nutrition — he brings regulated product development, clinical data analysis, and evidence-based content standards to every tool and article on this site.
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Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before making changes to your diet, exercise, or supplement routine.