How a calorie deficit works
You lose weight when you eat fewer calories than your body uses. This calculator estimates how many calories you burn in a day, then subtracts a deficit that matches the pace you choose, from half a pound to two pounds a week. It also shows how many weeks it should take to reach your goal.
The method
- Basal metabolic rate (BMR), with the Mifflin-St Jeor equation: 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5 for men, or − 161 for women.
- Maintenance calories (TDEE) = BMR × activity factor, from 1.2 for a desk job to 1.9 for very physical work.
- Daily deficit = pounds per week × 3,500 ÷ 7: about 500 kcal for 1 lb a week.
- Calorie target = TDEE − deficit.
- Weeks to goal = pounds to lose ÷ pounds per week.
Worked example
A 35-year-old man weighs 180 lb, is 5 ft 10 in and lightly active. He wants to reach 165 lb at 1 lb a week.
- BMR: 10 × 81.6 + 6.25 × 177.8 − 5 × 35 + 5 = 1,758 kcal.
- TDEE: 1,758 × 1.375 = 2,417 kcal.
- Deficit: 1 × 3,500 ÷ 7 = 500 kcal.
- Target: 1,917 kcal a day.
- Time: 15 lb ÷ 1 = 15 weeks, about 3.5 months.
Target by pace
| Pace | Calories a day | Weeks to lose 15 lb |
|---|---|---|
| 0.5 lb a week | 2,167 | 30 |
| 1 lb a week | 1,917 | 15 |
| 1.5 lb a week | 1,667 | 10 |
| 2 lb a week | 1,417 | 7.5 |
Choosing a pace
A pace of 0.5 to 1 lb a week is easier to keep up and protects muscle. Two pounds a week is a maximum for most people and works best for those with more weight to lose. Health organizations suggest not going below about 1,500 kcal a day for men and 1,200 kcal for women without medical supervision; the calculator flags targets under those levels.
Why progress slows
As you lose weight, your BMR and the energy you spend moving both drop. The 3,500 kcal rule also ignores water shifts, which can hide fat loss for a week or two. Weigh yourself at the same time of day, look at the weekly average, and recalculate your target every 10 lb or so.
Making the deficit easier
- Protein: aim for at least 1.2 g per kg of body weight to keep muscle and stay full.
- Strength training: two or three sessions a week help preserve muscle mass.
- Sleep: short nights increase hunger hormones.
- Fiber and volume: vegetables, fruit, legumes and whole grains fill you up for fewer calories.
This calculator gives general estimates. People with a medical condition, pregnant or breastfeeding women and teenagers should get personalized advice from a doctor or registered dietitian.