Calorie Deficit for Weight Loss 2026: How to Calculate Yours
By the 3Tej Research Desk · Published May 23, 2026 · 3 min read
- 1 lb of fat = approximately 3,500 calories
- 500 calorie/day deficit → 1 lb/week loss
- Maximum sustainable deficit: 20-25% below TDEE
- TDEE = BMR × activity multiplier
- Crash deficits (>1000 cal) cause muscle loss, metabolic adaptation, and rebound
Weight loss is, at the level of calories in versus calories out, a straightforward energy balance equation. Eat less than you burn over enough days and your body breaks down fat stores to make up the gap. The complication is figuring out what you actually burn (your Total Daily Energy Expenditure, or TDEE), how big a deficit your body and life can sustain, and how to track the moving target as your weight changes. This guide answers all three.
The 3,500 calorie per pound rule
One pound of body fat stores approximately 3,500 calories of energy. To lose one pound of fat, you need to be in a 3,500 calorie cumulative deficit across whatever time horizon makes that sustainable. Spread over a week: 500 calories per day. Spread over two weeks: 250 calories per day.
The 3,500 number is an approximation; the real range is 3,400 to 3,600 depending on body composition. Close enough for planning.
The rule applies to FAT loss. Early weeks of any deficit show much larger scale-weight changes (5 to 10 lbs in week 1 is common) because of glycogen and water depletion, not fat. The 1 lb per week target stabilizes after week 3 to 4.
Calculate your TDEE
Two steps: BMR (basal metabolic rate, calories burned at complete rest) then activity multiplier.
Mifflin-St Jeor BMR formula:
- Men: BMR = 10 × weight (kg) + 6.25 × height (cm) - 5 × age + 5
- Women: BMR = 10 × weight (kg) + 6.25 × height (cm) - 5 × age - 161
Then multiply BMR by activity factor: 1.2 sedentary (desk job, no exercise), 1.375 light (1 to 3 days/week light exercise), 1.55 moderate (3 to 5 days/week), 1.725 hard (6+ days/week), 1.9 athlete (twice daily). For most office workers with 3 to 4 gym sessions per week, use 1.4 to 1.5.
TDEE worked examples
| Profile | BMR | Activity | TDEE |
|---|---|---|---|
| Woman, 30, 65 kg, 165 cm, sedentary | 1,398 cal | 1.2 | 1,678 cal |
| Woman, 30, 65 kg, 165 cm, moderate | 1,398 cal | 1.55 | 2,167 cal |
| Man, 35, 80 kg, 178 cm, sedentary | 1,728 cal | 1.2 | 2,074 cal |
| Man, 35, 80 kg, 178 cm, moderate | 1,728 cal | 1.55 | 2,678 cal |
| Man, 25, 90 kg, 183 cm, hard activity | 1,938 cal | 1.725 | 3,343 cal |
For weight loss at 1 lb/week, subtract 500 from TDEE. For weight loss at 0.5 lb/week (more sustainable for last 10 to 20 lbs), subtract 250.
Sustainable deficit ranges
Bigger deficits do not mean faster fat loss in practice. The body adapts:
- 10 to 20% below TDEE. The sustainable sweet spot. Roughly 250 to 500 calories per day. Slow but durable. Most lean tissue preserved.
- 20 to 25% below TDEE. Aggressive but still defensible for adults with significant body fat. Beyond this, muscle loss accelerates and hunger becomes hard to manage.
- Above 25% below TDEE. Crash deficit. Loses fat AND muscle. Triggers metabolic adaptation (your TDEE drops as your body conserves energy). Hunger hormones go up. Rebound weight gain becomes likely.
- Below 1,200 cal/day (women) or 1,500 cal/day (men). Generally not recommended without medical supervision. Hard to hit micronutrient targets at this intake.
Why your weight stalls (and how to break it)
Three common reasons weight loss plateaus despite a calculated deficit:
- You lost weight. A smaller body burns fewer calories. The 500 calorie deficit you calculated at 80 kg is only a 300 calorie deficit at 70 kg. Recalculate TDEE every 5 kg of weight change.
- Activity dropped. NEAT (Non-Exercise Activity Thermogenesis: fidgeting, walking, standing) decreases unconsciously when you eat less. The 'sedentary' label might now apply when 'lightly active' did before.
- Tracking error. Self-reported calorie intake under-counts by 20 to 40% on average, per multiple studies. Food labels can be off by 20% legally. Recheck portions for a week with a kitchen scale and you will usually find the missing calories.
Diet break protocol: every 6 to 8 weeks of dieting, eat at maintenance for 1 to 2 weeks. Lets hormones recover, gives mental relief, and often resumes loss faster than continuous deficit.
Frequently asked questions
How much of a calorie deficit do I need to lose 1 pound a week?
Approximately 500 calories per day, since one pound of fat contains roughly 3,500 calories and 500 × 7 days = 3,500. Spread the deficit over a longer period for slower but more sustainable loss; a 250 cal/day deficit produces roughly half a pound per week of loss.
What is TDEE?
Total Daily Energy Expenditure: the total calories your body burns in a typical day, including basal metabolism (BMR) plus activity. The Mifflin-St Jeor formula estimates BMR; multiplying by an activity factor (1.2 sedentary to 1.9 athlete) estimates TDEE. Most calorie deficits are calculated against TDEE.
Is a 1000 calorie deficit safe?
Generally not for adults below an overweight BMI. A 1000 calorie deficit can be sustainable for short periods at higher body fat percentages but typically causes excess muscle loss, hunger hormone dysregulation, and metabolic adaptation that makes future maintenance harder. 20% deficit (typically 400 to 600 cal) is a more sustainable target.
Why is my weight loss slower than the calculator says?
Three usual reasons: (1) you lost weight, your new TDEE is lower than the original calculation; (2) NEAT (non-exercise activity) dropped, reducing total burn; (3) calorie intake under-reporting (self-tracked intake is reliably 20 to 40% lower than actual intake unless you weigh every meal). Recheck TDEE every 5 kg of weight change.
Should I eat back exercise calories?
Usually NO if you used a TDEE multiplier above 1.2 (sedentary). The multiplier already includes exercise. Eating back tracked exercise calories on top of an activity-included TDEE double-counts and erodes your deficit. Eat back exercise only if your TDEE calculation used the BMR (sedentary 1.2) factor.
Related calculators
Related guides
Sources and methodology
Numbers on this page are sourced from official government / regulator websites and refreshed automatically every Sunday by our build pipeline. Hover any number with a dotted underline to see its source and as-of date.
Tax authorities cited (8 jurisdictions)
Methodology: each calculator linked from this post documents its formula. Live market data (FX, treasury yields, mortgage rates) is pulled from public APIs (exchangerate.host, FRED, BoE, ECB, BoC, CoinGecko, stooq).