Weight Loss Calculator
Get your personal daily calorie target, macro split, and a week-by-week projection to reach your goal weight. Enter your details and the calculator works out your maintenance calories via the Mifflin-St Jeor formula, then builds a safe, sustainable plan around your chosen pace.
Formula
Worked example
Male, 35 years, 175 cm, 80 kg, moderately active: BMR = 10 × 80 + 6.25 × 175 - 5 × 35 + 5 = 1,768 kcal/day. TDEE = 1,768 × 1.55 = 2,740 kcal/day. To lose 8 kg in 12 weeks: 8 × 7,700 / 12 / 7 = 733 kcal/day deficit. Daily target = 2,740 - 733 = 2,007 kcal/day, losing ~0.67 kg/week.
How your maintenance calories (TDEE) are calculated
The calculator uses the Mifflin-St Jeor equation, the most widely validated BMR formula for the general population, to estimate how many calories your body burns at complete rest. It then multiplies by a Physical Activity Level (PAL) factor that reflects how much extra energy you burn through daily movement and exercise, from 1.2 for a desk-bound lifestyle to 2.1 for elite athletes. The result is your Total Daily Energy Expenditure (TDEE), the number of calories you need to eat to stay at your current weight. Because TDEE depends on body weight, it falls as you lose weight, which is why the schedule table shows slightly decreasing calorie targets week by week.
How the calorie deficit and target are derived
Body fat stores roughly 7,700 kcal per kilogram (about 3,500 kcal per pound). Multiplying your total weight to lose by that figure gives the total calorie deficit you need to create. Spreading it evenly over the weeks and days in your timeframe gives the required daily deficit, which is subtracted from your TDEE to produce your daily calorie target. The macro split then divides those calories among protein, carbohydrates, and fat. A higher protein share (30% is the default) helps preserve lean muscle during a deficit, while the remaining calories are split equally between carbs and fat.
Choosing a safe and sustainable pace
The CDC recommends losing 0.45-0.9 kg (1-2 lb) per week because slower rates preserve more muscle, leave you better nourished, and are far more likely to result in permanent fat loss. A daily deficit above 1,000 kcal is generally considered the upper safety limit by most dietary guidelines. If your current plan exceeds this, either extend the timeframe or increase your activity level. The calculator also estimates your new maintenance calories at goal weight so you have a realistic target for the maintenance phase once you arrive.
Why real-world results differ from the model
The 7,700 kcal-per-kilogram rule is a planning average. Real weight change is affected by water retention, glycogen stores, hormonal cycles, and progressive metabolic adaptation (your body becomes more efficient as weight falls). Day-to-day scale readings can swing by a kilogram or more for reasons unrelated to fat. Track your weight as a 7-day rolling average, reassess your TDEE every four to six weeks, and adjust your target if the actual trend diverges from the plan.
Choosing the right BMR formula
This calculator offers three formulas. Mifflin-St Jeor (the default) is the most accurate for the majority of the population, confirmed by multiple independent validation studies. The Revised Harris-Benedict formula (1984) is a reliable second option. The Katch-McArdle formula is the most accurate option for athletes or anyone with a lean physique because it is based on lean body mass rather than total body weight, but it requires an accurate body fat percentage measurement. All three formulas lose precision at the extremes of age, height, or adiposity.
Weekly pace, daily deficit, and safety band
| Weekly loss | Daily deficit | Pace |
|---|---|---|
| 0.25 kg (0.5 lb) | ~275 kcal | Gentle |
| 0.45 kg (1 lb) | ~495 kcal | Healthy |
| 0.7 kg (1.5 lb) | ~770 kcal | Moderate |
| 0.9 kg (2 lb) | ~990 kcal | High |
| 1.0 kg (2.2 lb) | ~1,100 kcal | Aggressive |
Approximate daily calorie deficit for common weekly loss rates (using 7,700 kcal/kg). Rates above 0.9 kg/week require careful monitoring.
Frequently asked questions
Do I need to know my maintenance calories to use this calculator?
No. Unlike many calculators that ask you to enter your TDEE, this tool calculates it for you from your age, sex, height, weight, and activity level using the Mifflin-St Jeor equation. You can also switch to the Revised Harris-Benedict or Katch-McArdle formula in the advanced options.
How many calories should I cut to lose 1 kg per week?
One kilogram of body fat stores roughly 7,700 kcal, so a weekly loss of 1 kg requires a deficit of about 7,700 kcal per week, or about 1,100 kcal per day. That approaches the upper safe limit. Most people do better aiming for 0.5-0.7 kg per week, which needs only a 550-770 kcal/day deficit.
Why does the schedule show calorie targets getting lower each week?
As you lose weight your BMR falls because a lighter body burns fewer calories at rest. The same activity multiplier applied to a lower BMR means a lower TDEE, so the daily target needed to maintain the same weekly rate drops slightly over time. The schedule table models this progressive adjustment. In practice, recalculate every 4-6 weeks rather than adjusting every single week.
What is the Katch-McArdle formula and when should I use it?
The Katch-McArdle formula estimates BMR from lean body mass rather than total body weight. This makes it more accurate for lean or athletic individuals whose high muscle mass would otherwise be undervalued by formulas that rely on total weight. You will need a body fat percentage reading from a DEXA scan, hydrostatic weighing, or a calibrated body fat calculator.
How much protein should I eat when losing weight?
Research consistently shows that a higher protein intake (roughly 1.6-2.4 g per kilogram of body weight, or about 30-35% of total calories) during a calorie deficit helps preserve muscle mass, increases satiety, and raises the thermic effect of feeding. This calculator defaults to 30% of calories from protein, which is a good starting point for most people.
Is it safe to lose weight quickly?
The CDC advises losing weight gradually at 0.45-0.9 kg (1-2 lb) per week. Rapid loss at more than 1 kg per week risks significant muscle loss, nutrient deficiencies, gallstones, and metabolic adaptation that makes keeping the weight off harder. If your plan flags an aggressive pace, lengthen the timeframe.
What should I eat at goal weight to maintain it?
The calculator shows your estimated maintenance calories at goal weight in the results. This is your new TDEE after losing the weight, assuming the same activity level. It will be lower than your current TDEE because a lighter body burns less energy, so plan to eat somewhat less than you do today to stay at goal weight.