This works out what to eat rather than what you burn. It starts from your total daily energy expenditure, applies the deficit or surplus your goal requires, and refuses to return a target so low that eating adequately becomes impossible.
- What it gives you
- A daily calorie target
- Based on
- Mifflin-St Jeor BMR × activity ± goal
- Energy per pound of fat
- About 3,500 calories
- Intake floor
- 1,200 women · 1,500 men
- Sustainable rate
- 0.5–1 lb per week
Formula
Mifflin-St Jeor with the 3,500 kcal/lb energy-balance ruleTarget = TDEE + (rate in lb/week × 3,500 ÷ 7) TDEE = BMR × activity factor
- TDEE
- — Total daily energy expenditure — your maintenance level
- rate
- — Desired weekly weight change; negative to lose
- 3,500
- — Approximate calories stored in one pound of body fat
The 3,500-calorie rule is a linear approximation. It predicts short-term change well but overstates long-term loss, because expenditure falls as body mass does. Recalculate every 5–10 lb.
Calorie Calculator examples
| Input | Result | Category |
|---|---|---|
| Woman, 30, 5'5", 150 lb, lose 1 lb/wk | 1,672 cal/day | Moderate deficit |
| Woman, 30, 5'5", 150 lb, maintain | 2,172 cal/day | Maintenance |
| Man, 30, 5'10", 180 lb, lose 1 lb/wk | 2,263 cal/day | Moderate deficit |
| Man, 30, 5'10", 180 lb, maintain | 2,763 cal/day | Maintenance |
| Man, 25, 6'0", 160 lb, gain 0.5 lb/wk | 3,267 cal/day | Surplus |
| Woman, 45, 5'4", 180 lb, lose 1.5 lb/wk | 1,200 cal/day | Moderate deficit |
How many calories should I eat to lose weight?
A deficit of 500 calories a day predicts about a pound a week, and that is the rate most guidelines point to as the balance between meaningful progress and sustainability.
| Daily deficit | Predicted loss | Trade-off |
|---|---|---|
| 250 cal | 0.5 lb/week | Easiest to sustain; slow but preserves lean mass well |
| 500 cal | 1 lb/week | The standard recommendation for most people |
| 750 cal | 1.5 lb/week | Noticeably harder; hunger and fatigue become factors |
| 1,000 cal | 2 lb/week | Only appropriate at higher starting weights |
Deficit size should scale with body size. Two pounds a week is reasonable for someone at 300 lb and unsustainable for someone at 140 lb. A useful rule of thumb is to keep the weekly deficit under about 1% of body weight.
Why the calculator will not go below a floor
If your requested rate would push intake below roughly 1,200 calories for women or 1,500 for men, the target is raised to that floor and flagged.
Below those levels, hitting protein, calcium, iron, and B-vitamin requirements from food alone becomes very difficult. Sustained very low intakes also accelerate the metabolic adaptation that makes further loss harder, and increase the share of weight lost that comes from muscle rather than fat.
Why weight loss stalls
Almost everyone stalls eventually, and the reasons are predictable rather than mysterious.
- Your TDEE has fallen. A lighter body costs less to maintain and less to move, so the same intake is now a smaller deficit.
- Spontaneous movement drops. In a deficit people unconsciously fidget less, walk less, and sit more — often hundreds of calories a day.
- Portion creep. Self-reported intake drifts upward over weeks without any conscious decision; measured underreporting is commonly 20–30%.
- Water masks fat loss. Glycogen, sodium, and hormonal cycles move scale weight by several pounds independently of fat.
The fix for the first is arithmetic — recalculate. For the rest it is measurement: weigh food for a fortnight, weigh yourself under identical conditions, and judge the trend over weeks rather than days.
Calories to gain weight
A surplus of 250–500 calories a day supports roughly half a pound to a pound of gain per week. Going substantially higher does not build muscle faster; it adds fat.
Muscle accrues slowly even under ideal conditions — perhaps 0.25–0.5 lb per week for a beginner, less for the trained. Pair the surplus with resistance training and adequate protein, or the gain will be mostly fat.
Do calories alone determine weight?
Energy balance determines weight change. But calories are not equally easy to adhere to, and that is where diet composition matters.
Protein has the highest thermic effect and the strongest effect on satiety, so higher-protein diets tend to produce better adherence and preserve more lean mass at the same calorie level. Fibre-rich whole foods are more filling per calorie than refined ones. None of this repeals energy balance — it makes hitting the target easier.
Frequently asked questions
How many calories should I eat a day to lose weight?
Take your maintenance calories and subtract 500 for about a pound a week. For most adults that lands between 1,400 and 2,000 calories, but it depends entirely on your size and activity — use the calculator above rather than a generic figure.
Is 1,200 calories a day too low?
For most adult women it is the practical floor rather than a target, and for men it is too low. Below that, meeting protein and micronutrient needs from food becomes difficult, and the diet is hard to sustain long enough to matter.
How long will it take me to lose 20 pounds?
At a 500-calorie daily deficit, roughly 20 weeks. Expect it to take longer than the arithmetic suggests, because your expenditure falls as you lose weight and progress slows toward the end.
Do I need to count calories to lose weight?
No, but you do need a deficit. Counting is one way to create one reliably; portion control, higher protein intake, and cutting liquid calories work for many people without tracking. Counting for a few weeks is useful mainly for calibrating your sense of portion size.
Why am I not losing weight in a calorie deficit?
The most common reasons are underestimating intake, overestimating activity, and a TDEE that has fallen as you lost weight. Judge over three to four weeks, since water-weight fluctuations easily mask two weeks of real fat loss.
Should I eat more on workout days?
You can, but it is not necessary. Weight change responds to the weekly total, so most people find it simpler to eat a consistent daily amount and let training days and rest days average out.
Sources
- A new predictive equation for resting energy expenditure in healthy individuals — Mifflin et al., American Journal of Clinical Nutrition, 1990
- Guidelines (2013) for Managing Overweight and Obesity in Adults — AHA/ACC/TOS, published in Obesity, 2014
- Quantification of the effect of energy imbalance on bodyweight — Hall et al., The Lancet, 2011
- Dietary Guidelines for Americans, 2020–2025 — US Departments of Agriculture and Health and Human Services, 2020