BodyCalWhat this calorie deficit calculator does
This calculator answers the three questions every weight loss plan depends on: how many calories your body burns each day (your maintenance calories, or TDEE), how many you should eat to lose weight at your chosen pace, and when you'll reach your goal. Instead of a single number, you get an interactive week-by-week forecast, milestone predictions at 25%, 50%, and 75% of your journey, and a projected goal completion date.
Everything updates instantly as you adjust your inputs, so you can compare scenarios — what happens if you pick a gentler rate, or move from a sedentary to a lightly active lifestyle — before committing to a plan.
How the formula works
We start with the Mifflin–St Jeor equation, the formula recommended by the Academy of Nutrition and Dietetics for estimating resting metabolic rate:
- Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
- Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
Your BMR is then multiplied by an activity factor between 1.2 (sedentary) and 1.9 (very active) to produce your Total Daily Energy Expenditure (TDEE) — the calories you burn in a real day, including movement and exercise. Your chosen weight loss rate is converted to a daily deficit using the well-established approximation of ~7,700 kcal per kilogram of body fat (≈3,500 kcal per pound), and that deficit is subtracted from your TDEE to give your recommended daily intake.
A worked example
Take a 32-year-old woman, 168 cm tall, weighing 82 kg, lightly active, aiming for 70 kg at 0.5 kg per week. Her BMR works out to about 1,539 kcal. Multiplied by the light-activity factor of 1.375, her TDEE is roughly 2,116 kcal/day. Losing 0.5 kg per week requires a daily deficit of about 550 kcal, giving a target of ~1,566 kcal/day and a projected goal date about 24 weeks out — with the halfway milestone (76 kg) arriving around week 12.
Why a moderate deficit beats an aggressive one
Large deficits look attractive on paper but consistently underperform in practice. Research on dietary adherence shows the deficit you can sustain beats the deficit that looks fastest. Moderate deficits (15–25% below TDEE) preserve more lean muscle, keep training quality higher, cause less hunger-driven rebound eating, and produce smaller drops in resting metabolism. They also leave room for real life — meals out, holidays, and the occasional bad week — without derailing the plan.
Common mistakes to avoid
- Double-counting exercise.If you selected an activity level that includes your workouts, don't also "eat back" exercise calories from a fitness tracker.
- Never recalculating. A lighter body burns fewer calories. Re-run your numbers every 5–7 kg lost or your progress will quietly stall.
- Judging by daily weigh-ins. Day-to-day scale weight swings 1–2 kg from water, salt, and glycogen. Track weekly averages instead.
- Ignoring protein. Aim for roughly 1.6–2.2 g of protein per kg of goal weight to protect muscle while in a deficit.
- Going below the floor. Intakes under 1,200 kcal (women) or 1,500 kcal (men) make adequate nutrition very difficult and should only happen under medical supervision.
How to use your results
Set your recommended intake as a daily budget, hit it within ±100 kcal most days, and weigh yourself 3–4 mornings a week, comparing weekly averages. After three to four weeks, compare your real rate of loss to the forecast chart above: if you're slower than predicted, tighten portions or reduce intake by 100–150 kcal; if you're much faster or feel drained, add calories back. Pair your plan with our BMI calculatorto track which category you're moving toward, and the water intake calculator — hydration needs shift as training volume changes.