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Weight-loss calculator
Enter your details and a target weight. The calculator estimates how many calories you burn, follows your weight day by day as your needs fall, and shows the date you reach the target as a chart and a table.
Your plan
Target date
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- BMR
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- Maintenance (TDEE)
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- Deficit on day 1
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- First week
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- BMI
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- Linear estimate
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Things to keep in mind
An estimate, not medical advice. Real weight moves up and down with water and glycogen from day to day, and 7,700 kcal per kilogram is an approximation: static rules like it overestimate long-term loss (Hall et al., 2011). Recomputing BMR as your weight falls captures part of that, but not the further drop in energy use the body makes while dieting. Age, height and activity stay as entered.
Plan table
| Date | Day | Weightkg | Lostkg | BMRkcal | Maintenancekcal | Eatenkcal | Deficitkcal | BMI |
|---|
Every day of the plan, for Excel or any spreadsheet.
How it is calculated
Basal metabolic rate
The basal metabolic rate (BMR) is the energy your body uses in a day at rest, just to keep going. By default the calculator uses the Mifflin–St Jeor equation (Mifflin et al., 1990), with weight w in kilograms, height h in centimeters and age a in years:
BMRmen = 10w + 6.25h − 5a + 5
BMRwomen = 10w + 6.25h − 5a − 161
The revised Harris–Benedict equation (Roza & Shizgal, 1984) is 88.362 + 13.397w + 4.799h − 5.677a for men and 447.593 + 9.247w + 3.098h − 4.33a for women. Katch–McArdle uses lean body mass instead of weight: 370 + 21.6 × lean mass. Over the plan, a quarter of each kilogram lost is taken to be lean mass (Forbes’s rule of thumb), so with this equation BMR falls by 5.4 kcal for every kilogram lost.
Maintenance calories, the total daily energy expenditure (TDEE), are BMR times the physical activity level (PAL), from sedentary to extra active 1.2, 1.375, 1.55, 1.725, and 1.9:
TDEE = BMR × PAL
From calories to kilograms
Each kilogram lost is taken to be worth about 7,700 kcal. On every day n, what you eat (I) is subtracted from maintenance at that day’s weight, and the deficit is turned into kilograms:
wn+1 = wn − TDEE(wn) − I7,700
The next day BMR is recomputed from the new weight, so maintenance falls as you lose weight, and if you keep eating the same amount, the deficit shrinks a little every day. In “Daily deficit” mode the deficit is held fixed by definition: weight falls in a straight line, and what you eat falls instead. Age, height and activity stay as entered for the whole plan.
With a fixed intake, weight stops falling where maintenance equals what you eat. For Mifflin–St Jeor that equilibrium weight is (with s = 5 for men and s = −161 for women)
w* = I/PAL − 6.25h + 5a − s10
If the target is at or below this weight, it is never reached at that intake, and the curve on the chart levels off toward it. The other two equations are also straight lines in weight, so they give a closed form in the same way.
The 7,700 kcal per kilogram rule is an approximation. Hall et al. (2011, The Lancet) showed that static rules like it overestimate long-term weight loss. Recomputing BMR every day captures part of that slowdown, but not adaptive thermogenesis, the further drop in energy use the body makes while dieting. Read the result as an estimate.
Tips
Pick your activity level honestly. Most people think they move more than they do. If you are between two levels, take the lower one; if you lose faster than planned, you can move up later.
Why the curve flattens. A lighter body uses less energy, so the same meals make a smaller deficit each week. That is why the plan takes longer than the dashed straight line, which keeps the first day’s deficit forever.
The scale moves every day. Water, salt, glycogen and what is still being digested can change your weight by a kilogram or more overnight. Compare weekly averages, not single mornings.
Weigh yourself the same way. Same scale, same time: in the morning, after the bathroom, before eating or drinking. Then the numbers can be compared.
Keep your muscle. Enough protein and some strength training help you keep lean mass while you lose fat, and lean mass keeps your BMR from falling as much.
Start again from where you are. Every few weeks, enter your current weight and today’s date. The plan then starts from your real weight instead of the projected one.