Deficitly
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What is a calorie deficit?
A calorie deficit means eating fewer calories than your body burns. Your body makes up the gap from stored energy, mostly fat, so you lose weight. For example, a 40-year-old woman of 70 kg (154 lb) who walks 8,000 steps a day burns about 1,890 calories. If she eats 1,500, she's in a deficit of 390 calories a day and loses about 0.35 kg (0.8 lb) a week. There's no special food or timing involved: any diet that works does it by creating a deficit.
How a calorie deficit works
Your body needs energy every day to keep you alive and moving. That total is your maintenance, or TDEE. Eat exactly that and your weight stays the same. Eat less and your body takes the rest from its stores: some glycogen and water in the first days, then mostly fat. About 7,700 calories of deficit add up to 1 kg of body fat (3,500 per pound, roughly), so a deficit of 500 a day loses about 0.5 kg (1.0 lb) a week. This is the "calories out" side of calories in, calories out. Typical numbers by age and sex: how many calories do I burn a day.
Where your calories go
| Part | Calories | Share |
|---|---|---|
| Resting (BMR) | 1,370 | 73% |
| Daily life | 140 | 7% |
| Steps | 190 | 10% |
| Digesting food | 190 | 10% |
| Total | 1,890 | 100% |
Most of your burn happens at rest, which is why a deficit mostly comes from eating less. Steps are the part you control most easily (NEAT). Get your own numbers from the TDEE calculator. Your resting part on its own: BMR calculator.
How to start a calorie deficit in 5 steps
- Find your maintenance with the box above or the maintenance calorie calculator. Use your real average steps, not a hopeful "active".
- Pick a pace: 0.5% of your weight a week is steady, up to 1% is possible (how much to lose a week).
- Set your calories: maintenance minus the deficit, never below 1,200 (women) or 1,500 (men). The calorie deficit calculator does the maths.
- Keep protein high (about 1.6–2.2 g per kg of a healthy weight) so you lose fat rather than muscle; the calorie deficit meal plan shows what a day looks like.
- Weigh in a few times a week and compare weekly averages. After 3–4 weeks, adjust by 100–200 calories if the trend doesn't match the plan.
Eat less or move more?
| Change | Calories a day |
|---|---|
| Cook with 1 tbsp less oil | 120 |
| Skip 2 tbsp peanut butter | 190 |
| Swap 1 cup of rice for 1 cup of broccoli | 150 |
| A 30-minute brisk walk | 130 |
| 3,000 more steps a day | 70 |
Food changes are usually the easier lever: one swap can match a half-hour walk. But steps keep your burn from sliding while you diet, so most people do best with a moderate cut in food plus a few thousand more steps. Watch out for counting exercise twice: see should you eat back exercise calories? To see what a walk at your speed burns, try the walking calorie calculator. More swaps and the lowest-calorie foods: low-calorie foods. Tracking it day to day: how to count calories. Does fasting help? Does intermittent fasting work?
How do you know you're in a calorie deficit?
Your weight trend tells you. If your weekly average weight is falling over 2–3 weeks, you're in a deficit, whatever your app says. Hunger isn't proof: you can be hungry at maintenance and comfortable in a deficit. Daily weight jumps by 1–2 kg with water and salt, so single weigh-ins mislead (why your weight fluctuates). To turn your start and current weight into % lost and % a week, use the weight loss percentage calculator.
Common mistakes
- Underestimating what you eat. In a classic study, people who said they couldn't lose weight ate about 47% more than they reported. Weigh food for a couple of weeks.
- Weekends. Two big days can cancel five careful ones.
- Too big a deficit. It's hard to stick to and costs muscle; see 500-calorie deficit.
- Expecting a straight line. Loss slows as you get lighter; see calorie deficit but not losing weight.
Is a calorie deficit safe?
A moderate deficit is safe for most healthy adults. It isn't for children and teens, during pregnancy or breastfeeding, with a history of eating disorders, or with a BMI under 18.5; in those cases talk to a doctor or dietitian first. Deficitly doesn't plan a deficit in any of those situations.
Sources
- Hall KD, Sacks G, Chandramohan D, et al. Quantification of the effect of energy imbalance on bodyweight. Lancet 2011;378(9793):826–837.
- Lichtman SW, Pisarska K, Berman ER, et al. Discrepancy between self-reported and actual caloric intake and exercise in obese subjects. N Engl J Med 1992;327(27):1893–1898.