What this calculator does
Most people know they need a calorie deficit to lose fat. Fewer know how big it should be or how long it will take. This tool answers both: it estimates the calories you burn each day, subtracts the deficit needed for your chosen pace and projects a finish date.
Seeing a realistic date up front helps. It turns a vague wish into a plan with a checkpoint, and it shows clearly why crash diets rarely save as much time as they promise.
How to use it
Enter your sex, age, height, current weight and goal weight, then pick the activity level that best describes a normal week. Finally choose a pace: 0.25, 0.5, 0.75 or 1 kg per week (about 0.5, 1, 1.5 or 2 lb).
The result shows your maintenance calories, your daily target, the number of weeks to your goal, the estimated date and the total deficit involved. If your target drops below a sensible floor, the calculator warns you.
The maths behind it
Maintenance calories come from the Mifflin-St Jeor equation, multiplied by your activity factor, the same approach used in the TDEE calculator.
Men: BMR = 10 × kg + 6.25 × cm − 5 × age + 5
Women: BMR = 10 × kg + 6.25 × cm − 5 × age − 161
Daily deficit = pace (kg/week) × 7,700 kcal / 7
Target = BMR × activity factor − daily deficit
Weeks to goal = (current − goal weight) / pace
The 7,700 kcal per kilogram figure (about 3,500 per pound) is the standard approximation for the energy in body fat tissue. A pace of 0.5 kg per week therefore needs a deficit of about 550 kcal a day.
Choosing a pace
| Pace | Daily deficit | Best for |
|---|---|---|
| 0.25 kg (0.5 lb) / week | ~275 kcal | Lean lifters, last few kilos, keeping strength |
| 0.5 kg (1 lb) / week | ~550 kcal | Most people; sustainable and muscle-friendly |
| 0.75 kg (1.5 lb) / week | ~825 kcal | Higher body fat, strong adherence |
| 1 kg (2 lb) / week | ~1,100 kcal | Larger bodies only; hard to sustain |
A useful rule is to lose about 0.5-1% of your body weight per week. Faster than that, especially when already lean, increases the risk of losing muscle, feeling flat in the gym and rebounding afterwards.
The calculator flags targets below 1,500 kcal for men and 1,200 kcal for women. Going lower is hard to meet nutritional needs on and should be done only with medical supervision.
Why the estimate drifts, and what to do
The projected date assumes your maintenance stays fixed. In reality it falls as you lose weight: a smaller body burns less, and your body adapts by reducing movement and, to a lesser extent, metabolic rate. This is called metabolic or adaptive thermogenesis. Kevin Hall's modelling work at the NIH showed that the simple 3,500 kcal rule overestimates long-term loss for this reason.
- Recalculate every 5 kg (about 10 lb) lost, using your new weight.
- Judge progress on weekly averages, not single weigh-ins. Water can move the scale 1-2 kg day to day.
- Plateaus of one or two weeks are normal. If the weekly average has not moved for three weeks, cut a further 100-200 kcal or add daily steps.
- Diet breaks of one to two weeks at maintenance every 8-12 weeks can make a long diet easier to stick to.
Keep protein high and keep lifting heavy. Those two habits do more than anything else to make sure the weight you lose is fat, not muscle.
A worked example
Take a 32-year-old woman, 165 cm tall, weighing 78 kg, who wants to reach 68 kg. She trains three times a week, so she picks the lightly active level (1.375).
BMR = 10 × 78 + 6.25 × 165 − 5 × 32 − 161 ≈ 1,490 kcal
Maintenance = 1,490 × 1.375 ≈ 2,050 kcal
At 0.5 kg per week her deficit is about 550 kcal, giving a daily target of roughly 1,500 kcal and a timeline of 20 weeks for 10 kg. At 1 kg per week the target would drop to about 950 kcal, well below the 1,200 kcal floor, and the calculator would warn her. A pace of 0.5 kg is the sensible choice.
After the first 5 kg she recalculates at 73 kg. Her maintenance has dropped to around 1,980 kcal, so her target becomes about 1,430 kcal to keep the same pace. Small adjustments like this, made on schedule, are what keep progress moving through the second half of a diet.
| Week | Expected weight | Daily target |
|---|---|---|
| 0 | 78 kg | ~1,500 kcal |
| 10 | 73 kg | ~1,430 kcal (recalculated) |
| 20 | 68 kg | Move towards new maintenance (~1,910 kcal) |
Reaching the goal is not the end. Increase calories gradually over two to four weeks to the new maintenance level rather than jumping straight back to old habits. That reverse step is where many people regain the weight.
Who should not use this alone
If you are pregnant or breastfeeding, under 18, have diabetes or another medical condition, take medication that affects appetite or blood sugar, or have a history of disordered eating, talk to a doctor or registered dietitian before starting a deficit. The calculator gives estimates for healthy adults only.
Next steps
Turn your calorie target into daily protein, carbs and fat with the macro calculator, and pick a training plan such as the fat loss workout plan. The full method, including tracking, is in how to calculate calories for weight loss.
Frequently asked questions
How many calories should I eat to lose 0.5 kg a week?
About 550 kcal less than your maintenance each day. For many adults that lands between 1,500 and 2,200 kcal, depending on size and activity.
Is losing 1 kg a week safe?
For people with a lot of weight to lose it can be, at least early on. For leaner people it usually means too much muscle loss and hunger. Around 0.5-1% of body weight per week is a safer guide.
Why am I not losing weight on my calorie target?
Common reasons are underestimated portions, weekend overeating, water retention and a maintenance estimate that is too high. Track carefully for three weeks, then lower your target by 100-200 kcal if needed.
Will my goal date be accurate?
Treat it as a best case. Your maintenance falls as you lose weight, so progress usually slows. Recalculate after every 5 kg to keep the estimate realistic.
What is the lowest calorie intake I should go to?
As a general rule, not below about 1,500 kcal for men or 1,200 kcal for women without medical supervision. Below that it is difficult to get enough protein, vitamins and minerals.
References
- Mifflin MD, St Jeor ST, Hill LA, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990.
- Hall KD, Sacks G, Chandramohan D, et al. Quantification of the effect of energy imbalance on bodyweight. Lancet. 2011.
- Helms ER, Aragon AA, Fitschen PJ. Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. J Int Soc Sports Nutr. 2014.
Results are estimates for healthy adults and are not medical advice. See our medical disclaimer.
