To calculate calories for weight loss, estimate your basal metabolic rate (BMR), multiply it by an activity factor to get your total daily energy expenditure (TDEE), then subtract a moderate deficit, usually about 500 calories a day or 15% to 25% of TDEE. For a 35-year-old woman who is 5 feet 5 inches tall, weighs 170 pounds and is lightly active, TDEE is about 2,017 calories, so eating around 1,500 to 1,700 calories a day should produce gradual weight loss. Expect the rate to slow as you lose weight, and adjust as you go.
Step 1: Estimate your BMR
BMR is the energy your body uses at rest. The Mifflin–St Jeor equation is the most widely recommended estimate for adults:
Convert first: pounds × 0.4536 = kilograms; inches × 2.54 = centimeters.
Example (woman): 170 lb = 77.11 kg; 5′5″ = 65 in = 165.1 cm; age 35.
BMR = 771.1 + 1,031.9 − 175 − 161 = 1,467 calories
For other BMR equations and when to use them, see how to calculate BMR, or run the BMR calculator.
Step 2: Multiply by an activity factor
| Activity level | Description | Multiplier |
|---|---|---|
| Sedentary | Desk job, little or no exercise | 1.2 |
| Lightly active | Light exercise 1–3 days a week | 1.375 |
| Moderately active | Moderate exercise 3–5 days a week | 1.55 |
| Very active | Hard exercise 6–7 days a week | 1.725 |
| Extra active | Physical job plus hard training | 1.9 |
Example: 1,467 × 1.375 = 2,017 calories a day to maintain current weight.
Most people overestimate their activity. If you are unsure between two levels, choose the lower one. The calorie calculator combines steps 1 and 2.
Step 3: Subtract a deficit
Two common ways to size the deficit:
| Approach | Daily target (example woman) | Initial weekly loss estimate |
|---|---|---|
| −250 calories | 1,767 | about 0.5 lb |
| −500 calories | 1,517 | about 1 lb |
| −750 calories | 1,267 | about 1.5 lb |
| −15% of TDEE | 1,715 | about 0.6 lb |
| −20% of TDEE | 1,614 | about 0.8 lb |
| −25% of TDEE | 1,513 | about 1 lb |
The weekly estimates use the traditional rule that about 3,500 calories equals one pound of body fat. A percentage deficit scales better: 500 calories is a modest cut for a 3,000-calorie TDEE but a steep one for 1,800.
Second example (man): 40 years old, 5′10″ (177.8 cm), 200 lb (90.72 kg), moderately active.
- BMR = 907.2 + 1,111.3 − 200 + 5 = 1,823
- TDEE = 1,823 × 1.55 = 2,826
- Target with a 500-calorie deficit: about 2,326 calories
Why the 3,500-calorie rule overpromises
The 3,500-calorie rule assumes that your energy needs stay constant. They do not. As you lose weight:
- A smaller body needs fewer calories, at rest and when moving.
- Your body adapts by burning slightly less energy than the smaller size alone predicts.
- Some of the weight lost is lean tissue and water, not only fat.
Researchers at the National Institutes of Health built a dynamic model of these effects; it underlies the NIH Body Weight Planner. A useful approximation from that work: every 10 calories per day of sustained change eventually moves body weight by about 1 pound, with roughly half of the change in the first year. A permanent 500-calorie daily cut therefore points toward an eventual loss of about 50 pounds over several years, not 52 pounds in one year as the 3,500-calorie rule would suggest.
In practice, recalculate every 10 to 15 pounds. When the example woman reaches 155 pounds, her BMR drops to about 1,399 and her TDEE to about 1,924, about 94 calories lower than at the start, so the same 1,517-calorie intake now produces a smaller deficit.
Safe limits
- Minimum intake: obesity guidelines from the National Heart, Lung, and Blood Institute and partner organizations suggest roughly 1,200 to 1,500 calories a day for women and 1,500 to 1,800 for men on a weight-loss plan. Going lower makes it hard to meet nutrient needs and should be medically supervised.
- Rate of loss: the CDC suggests aiming for about 1 to 2 pounds a week. Faster early losses are often water.
- Who should get medical advice first: anyone who is pregnant or breastfeeding, under 18, managing diabetes or taking medications that affect blood sugar or blood pressure, or with a history of disordered eating.
Making the deficit work
Protect muscle with protein and strength training
Higher protein intake and resistance exercise help preserve lean mass during a deficit, which keeps BMR higher. See how much protein do I need and split your calories with how to calculate macros or the macro calculator.
Account for exercise carefully
Exercise burns calories, but fitness trackers and machines often overestimate. If you add exercise calories back into your budget, consider adding back only half. The calories burned calculator estimates activity energy from standard MET values.
Track honestly for two weeks
Calorie labels and portion estimates have error. If your weight trend (averaged over a week or two, not day to day) is not moving after three to four weeks, reduce intake by another 100 to 200 calories or increase activity.
Plan the timeline
The weight loss calculator projects a timeline to a goal weight. Treat it as a range, and expect plateaus.
Quick summary
- BMR from Mifflin–St Jeor.
- TDEE = BMR × activity factor.
- Target = TDEE − 500 calories, or TDEE × 0.75 to 0.85.
- Stay above about 1,200 (women) or 1,500 (men) unless supervised.
- Recalculate every 10 to 15 pounds.
This guide is general information, not medical or nutrition advice. Calorie equations are estimates; individual needs vary. Talk with a doctor or registered dietitian before starting a weight-loss plan, especially if you have a health condition.
Frequently asked questions
How many calories should I eat to lose weight?
Estimate your total daily energy expenditure (TDEE) from your BMR and activity level, then subtract roughly 500 calories, or 15% to 25%. For a 35-year-old, 5-foot-5, 170-pound lightly active woman, TDEE is about 2,017 calories, so a target near 1,500 to 1,700 is reasonable.
Does a 3,500-calorie deficit equal one pound of fat?
Roughly, at the start, but the rule overpredicts long-term loss. As you lose weight your body burns fewer calories, so a fixed 500-calorie daily cut produces less than a pound a week over time. NIH researchers developed dynamic models that account for this slowdown.
What is the lowest safe calorie intake?
Federal obesity guidelines suggest weight-loss diets of about 1,200 to 1,500 calories a day for women and 1,500 to 1,800 for men. Very low-calorie diets of 800 or fewer calories should be used only under medical supervision.
How fast should I lose weight?
The CDC notes that people who lose weight gradually and steadily, about 1 to 2 pounds a week, are more successful at keeping it off. Faster loss early on is often water and glycogen, not fat.
Do I need to recalculate as I lose weight?
Yes. A smaller body burns fewer calories. Losing 15 pounds lowers the example woman's TDEE by about 94 calories a day, so revisit your numbers every 10 to 15 pounds or when progress stalls for several weeks.