Explore a calorie deficit from your starting estimate
A calorie deficit means taking in less energy than you expend over time. This calculator estimates maintenance calories, then subtracts a daily amount based on the weekly rate you select. The result is a planning scenario, not a measurement of your metabolism or a promise of weight loss.
Enter your body weight, height, age, formula setting, and usual activity. Choose kilograms or pounds and select a weekly rate to explore. A lower goal weight is optional; it adds a simple timeline estimate without changing the daily calorie calculation.
How the calorie deficit is calculated
The first step uses the Mifflin–St Jeor equation for resting energy expenditure. Online calculators often label this “BMR,” although resting and basal measurements use different conditions. Here, W is weight in kilograms, H is height in centimetres, and A is age in years:
Resting estimate = 10W + 6.25H − 5A + coefficient
The male equation uses +5; the female equation uses −161. “Prefer not to say” uses −78, the midpoint of those coefficients. That midpoint is a simplifying assumption, not a separately validated equation.
The calculator then multiplies the resting estimate by an activity factor to estimate total daily energy expenditure, or TDEE. It subtracts a daily deficit using the following arithmetic:
Daily deficit = weekly kg × 7,700 ÷ 7
Or: daily deficit = weekly lb × 3,500 ÷ 7
Daily calorie estimate = TDEE − daily deficit
Those calorie-per-weight factors are rough conversions. NIH research explains why a fixed 3,500-calorie rule does not capture how energy expenditure changes during weight loss. Brolic uses it to display the scenario’s arithmetic, not to predict an exact physiological response.
Choose an activity level for your whole week
Include work, walking, daily tasks, and exercise when choosing activity. Two people with the same gym schedule can still expend different amounts of energy across the day.
| Activity setting | Multiplier |
|---|---|
| Sedentary | 1.2 |
| Light | 1.375 |
| Moderate | 1.55 |
| Very active | 1.725 |
These are conventional planning multipliers added to the resting equation; they are not measured values. Exercise is already represented in the activity choice. Adding a second full workout-calorie estimate can count the same activity twice.
Follow the default inputs through the calculation
For an 80 kg, 180 cm, 30-year-old using the male equation and Moderate activity:
- Resting estimate: 10 × 80 + 6.25 × 180 − 5 × 30 + 5 = 1,780 kcal/day.
- Estimated maintenance: 1,780 × 1.55 = 2,759 kcal/day.
- Selected rate: 0.45 kg/week × 7,700 ÷ 7 = 495 kcal/day.
- Displayed daily estimate: 2,759 − 495 = 2,264 kcal/day.
For comparison, 1 lb/week uses a 500 kcal daily deficit. The kilogram and pound rate choices are rounded, so they do not produce perfectly identical results. Displayed weight, height, and calorie values are also rounded.
Treat targets and timelines as estimates
The optional timeline divides the difference between current and goal weight by the selected weekly rate, then rounds up to whole weeks. For example, 5 kg divided by 0.45 kg/week gives about 11.1 weeks, displayed as 12 weeks. It assumes a constant rate and does not model changes in energy needs, fluid balance, or adherence.
The NIDDK Body Weight Planner research describes models that account for changing metabolism and energy expenditure. This simpler calculator does not implement that dynamic model.
Brolic flags estimates below 1,500 kcal/day with the male setting and below 1,200 kcal/day with the other settings. These are screening flags, not personalized safety limits. A result above a flag is not automatically suitable, and a result below it should not be treated as an intake recommendation.
Review food records, comparable weight averages, and training performance over time rather than trying to validate the estimate from a single day. This tool is intended for general adult planning; medical conditions, pregnancy, eating-disorder recovery, and other individual nutrition needs require appropriate professional guidance.
Common questions
Is a 500-calorie deficit right for everyone?
No. In this calculator, 500 is simply the daily amount associated with the 1 lb/week selection. The same subtraction represents a different proportion of different people’s estimated maintenance needs.
Should I eat my BMR or my TDEE?
BMR is a resting estimate and TDEE includes the day’s activity. Neither automatically determines an appropriate eating target. This calculator uses TDEE as the starting point for the selected deficit scenario; the BMR vs. TDEE guide explains the distinction.
Does entering a goal weight change my calories?
No. Goal weight only affects the optional timeline. Current weight, height, age, formula setting, activity, and selected rate determine the daily estimate.
Why can actual weight change differ from the estimate?
Estimated intake and activity are imperfect, scale weight fluctuates, and energy expenditure can change over time. The selected rate is an assumption in this calculation, not a rate the tool can make your body follow.
Sources & method
Written by the Brolic team. These references explain the evidence and assumptions; this page does not replace individualized professional advice.
- Mifflin et al. — A predictive equation for resting energy expenditure — The resting-energy equation used in the first step.
- NIDDK — Research behind the Body Weight Planner — Why changing energy expenditure matters when modelling weight change.
- NIH — Body Weight Planner research brief — The limitations of treating 3,500 calories as a fixed prediction of one pound of weight loss.