Because you only gave a weight, we assumed a typical 35-year-old woman of 5'6" with a lightly active routine. Height and age change the answer: see the sensitivity table below, then enter your real numbers.
The calculation, step by step
1. Convert to metric
180 lb / 2.205 = 81.6 kg. 5'6" = 66 in x 2.54 = 167.6 cm.
2. BMR (Mifflin-St Jeor)
BMR = 10 x 81.6 + 6.25 x 167.6 - 5 x 35 - 161 = 1,528 calories. That is what the body burns at complete rest. The equation comes from Mifflin et al., Am J Clin Nutr 1990.
3. Multiply by activity (Lightly Active, x 1.375)
1,528 x 1.375 = 2,101 calories. Light exercise 1-3 days/week. This is TDEE, or maintenance calories.
4. Subtract (or add) for your goal
Cut: 2,101 - 500 = 1,601. Gentler cut: 2,101 - 250 = 1,851. The -500 target (1,601) stays above this profile's BMR (1,528), which is the practical floor to stay above.
Deficit and surplus table
| Goal | Calories / day | Expected weekly change |
|---|---|---|
| Lose (-500) | 1,601 | -1 lb / -0.45 kg |
| Lose (-250) | 1,851 | -0.5 lb / -0.23 kg |
| Maintain (0) | 2,101 | 0 lb / 0 kg |
| Gain (+250) | 2,351 | +0.5 lb / +0.23 kg |
Weekly change uses the common rule of thumb of about 3,500 calories per pound (7,700 per kg). It is an approximation: as you lose weight your needs fall, so real long-run change is slower (Hall et al., Lancet 2011). Suggested protein at this weight: about 162 g a day (0.9 g per lb).
If your activity is different
| Activity level | Multiplier | TDEE | Cut (-500) |
|---|---|---|---|
| Sedentary | 1.2 | 1,834 | 1,334 |
| Lightly Active | 1.375 | 2,101 | 1,601 |
| Moderately Active | 1.55 | 2,369 | 1,869 |
| Very Active | 1.725 | 2,636 | 2,136 |
| Extremely Active | 1.9 | 2,903 | 2,403 |
Most people overestimate their activity level. If you sit most of the day and train a few times a week, start from lightly active, not moderately active. Prefer counting steps? Convert steps to calories: at this size, every extra 1,000 steps burns roughly 32 calories, so 10,000 steps a day adds about 159 calories above a 5,000-step day.
How much height and weight matter
| Change | TDEE | Difference |
|---|---|---|
| 170 lb | 2,039 | -62 |
| 180 lb (this example) | 2,101 | - |
| 190 lb | 2,163 | +62 |
| 5'4" tall | 2,057 | -44 |
| 5'8" tall | 2,145 | +44 |
Ten pounds moves maintenance by about 62 calories, and two inches by about 44. Among women the same weight can mean a very different number, which is why a one-line answer to "how many calories should I eat" is only a starting point. Know your body fat? The calculator switches to Katch-McArdle, and the AI body fat estimator can give you the input from a photo.
What to do with this number
- Eat at 2,101 for two to three weeks and weigh yourself most mornings. Flat trend means the estimate is about right.
- To lose, start at 1,851 to 1,601. To gain slowly, try 2,351.
- Split it into protein, carbs and fat with the macro calculator, or turn it into a meal plan.
- Log it free in the baisics app, with a training plan built around these numbers: start free.