Your daily calorie target for weight loss = your Basal Metabolic Rate (BMR) × your activity level (total daily energy expenditure), minus a deficit tied to your target loss rate. Research supports a deficit of approximately 7,700 kcal per kg of body fat you aim to lose — or roughly 550 kcal/day to lose 0.5 kg/week.

"Eat less" is technically correct but practically useless without a number. Eat less than what? And by how much?

Consuming too few calories can backfire — your body adapts by slowing its metabolism, and you end up burning fewer calories at rest. Consume too many, and you simply won't lose weight. The right answer sits in a specific, personal range — and it starts with understanding how much energy your body actually needs.

Your Basal Metabolic Rate is the number of calories your body burns at complete rest — just to keep your organs functioning, your heart beating, and your temperature regulated.

The most widely validated equation for this is the Mifflin-St Jeor formula, which research consistently shows outperforms older calculations like Harris-Benedict in accuracy for both men and women.

Mifflin-St Jeor BMR Formula:

For example, a 35-year-old woman, 165 cm tall, weighing 75 kg would have a BMR of approximately 1,532 kcal/day.

Your BMR only accounts for rest. To get your Total Daily Energy Expenditure (TDEE) — the calories you actually burn each day — multiply your BMR by an activity factor:

Using the example above, a lightly active woman with a BMR of 1,532 would have a TDEE of ~2,107 kcal/day. That's what she needs to eat to maintain her current weight.

To lose weight, you need to consume fewer calories than you burn — creating a calorie deficit. But how big should that deficit be?

Research by Hall (2008), published in the International Journal of Obesity, established that approximately 7,700 kcal of deficit equates to losing 1 kg of body fat. This has become the standard basis for calculating weight loss timelines.

This translates practically to:

So for our example: a woman with a TDEE of 2,107 kcal, targeting 0.5 kg/week, should eat approximately 1,557 kcal/day.

You've probably heard that cutting 3,500 calories equals losing one pound (about 0.45 kg). This is a simplification that has been debunked. Hall (2008) demonstrated that this rule fails to account for metabolic adaptation — the way your body progressively reduces energy expenditure as you lose weight.

In practice, as you lose weight:

This is why a deficit that worked at the start may stall after several weeks. It's not willpower — it's physiology. Recalculating your TDEE every few weeks as your weight changes is how you stay on track.

A further study by Most & Redman (2020), published in Experimental Gerontology, confirmed that calorie restriction induces a reduction in energy expenditure larger than can be explained by body mass loss alone — a phenomenon called metabolic adaptation. Accounting for this is essential to realistic weight loss planning.

The research is clear: for weight loss, the total calorie deficit is the primary driver, not whether those calories come from fat, carbohydrates, or protein.

A landmark trial by Sacks et al. (2009) in the New England Journal of Medicine, comparing four diets with different fat, protein, and carbohydrate compositions, found that all groups lost similar amounts of weight when calories were equally reduced. The macronutrient split did not significantly change weight loss outcomes.

However, where macros do matter is how you feel during your deficit: adequate protein (above 0.8 g/kg/day, and ideally 1.0–1.2 g/kg) helps preserve muscle, reduces hunger, and supports metabolic health during weight loss (Wolfe et al., 2017, Advances in Nutrition).

Forkd uses the Mifflin-St Jeor equation as its BMR base, multiplied by your activity level to arrive at your TDEE. It then applies a deficit based on your chosen weight loss speed:

The app also enforces a safety floor (1,200 kcal for women, 1,500 kcal for men) to ensure you never drop to levels where micronutrient intake becomes dangerously inadequate — a real risk confirmed by Zhang et al. (2024) in Frontiers in Nutrition.

Your calorie goal recalibrates automatically as your weight changes, accounting for the metabolic adaptation the research warns about.

How do I know if my calorie calculation is accurate? The Mifflin-St Jeor formula is the most validated equation for estimating BMR, but it is still an estimate. Track your weight weekly for 3–4 weeks at a set calorie level — if the result doesn't match the predicted loss rate, adjust your intake by 100–150 kcal and monitor again. Real-world feedback is more accurate than any formula.

Should I eat back calories burned through exercise? If you use an activity multiplier (e.g., 1.55 for moderately active), your exercise is already factored into your TDEE. You should not additionally eat back all calories burned in a workout, as this leads to overestimation. Use the activity multiplier that best reflects your average week.

What if I am very active but trying to lose weight? Your TDEE will be higher, meaning your recommended daily intake can also be higher while still achieving a deficit. Active individuals should be especially careful not to cut calories too aggressively, as this risks muscle loss and reduced performance.

Why does my calorie goal change as I lose weight? As you lose weight, your BMR decreases because there is less body mass to maintain. TDEE falls with it. Recalculating every 5–10 kg of weight lost keeps your target accurate and avoids unnecessary plateaus.