TDEE and calorie deficit calculators both turn the same body inputs into daily calorie numbers, but they answer different questions. TDEE reports your estimated maintenance calories — what you would eat to keep weight roughly stable — and derives mild 10% deficit and surplus targets from it. The calorie deficit calculator takes the same kind of estimate and models what happens when you subtract a scenario amount you choose, such as 500 calories per day. One gives you a baseline with gentle targets; the other explores specific subtractions around a baseline.
What each calculator does
The TDEE calculator takes age, sex, height in centimeters, and weight in kilograms, plus an activity level. It computes basal metabolic rate with the Mifflin-St Jeor equation (male constant +5, female −161), multiplies by the activity factor you choose — sedentary 1.2 through very active 1.9 — and presents the result as maintenance calories, alongside a 10% deficit (TDEE × 0.9) and a 10% surplus (TDEE × 1.1). The defaults (male, 30, 175 cm, 70 kg, moderate) show a BMR of about 1,649, maintenance of 2,556, and targets of 2,300 and 2,811 kcal/day, all rounded to whole calories.
The calorie deficit calculator uses the same Mifflin equation and the same five activity factors, then subtracts a scenario you select: 250, 500, 750, or 1,000 calories per day. It reports BMR, TDEE, and the resulting scenario calories, and adds a static energy-equivalent line that divides seven days of the subtraction by 7,700 calories per kilogram (or 3,500 per pound) and multiplies by 4.33 — values the page identifies explicitly as product-defined scenario assumptions, not predictions of weight change. Its default example (male, 30, 75 kg, 178 cm, moderate, −500) shows BMR 1,718, TDEE 2,662, and scenario 2,162 calories.
Side-by-side
| TDEE calculator | Calorie deficit calculator | |
|---|---|---|
| Inputs | Age, sex, height, weight, activity level | Sex, age, height, weight, unit system, activity level, subtraction choice (250–1,000) |
| Primary output | Maintenance calories (TDEE), rounded to whole calories | Scenario calories after the selected subtraction |
| Secondary outputs | BMR, mild 10% deficit, mild 10% surplus | BMR, TDEE, static energy-equivalent mass line |
| Equation basis | Mifflin-St Jeor BMR × activity factor | Same Mifflin-St Jeor BMR × activity factor |
| How the deficit is chosen | Fixed at 10% of TDEE | User picks 250, 500, 750, or 1,000 calories to subtract |
| Range of the estimate | Adults; the page notes the equation was built from adult data | Ages limited to 18–100 |
| Stance | Educational estimate; weight-trend check suggested | Scenario arithmetic; explicitly not a prescription |
When to use which
Use the TDEE calculator when you want the baseline number: your estimated maintenance calories and a gentle starting target on either side. Its fixed 10% margins are deliberately mild, and the page walks through the weight-trend test — log intake, watch the scale, adjust from observations rather than trusting the formula indefinitely.
Use the calorie deficit calculator when you want to model a particular subtraction — for example, the common 500-calorie-per-day scenario — and see the arithmetic next to a static energy-equivalent figure. It is designed as a scenario-comparison workflow: pick one subtraction at a time, record TDEE and the amount, and treat the result as an estimate rather than an allowance. If you only need resting metabolism without activity, either page’s BMR line covers it, and both pages point to their underlying method rather than prescribing a diet.
Limits and disclaimer
Both pages are educational only and are not medical advice. The Mifflin-St Jeor equation predicts resting expenditure from population data and cannot see muscle mass, thyroid status, medication, or illness; activity factors are crude buckets that can shift the result by hundreds of calories. The TDEE page is explicit that its 10% cut is mild on purpose and that larger deficits carry different risks, while the calorie deficit page states that it cannot determine whether a deficit is appropriate and is not for children, pregnancy, eating-disorder recovery, or underweight users. Neither page forecasts actual weight change.