Daily calorie needs

This calculator uses the Mifflin-St Jeor equation, generally rated among the more accurate widely used BMR formulas for the general population:

• Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5
• Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) − 161

Weight and height both carry positive weight in the equation because a larger body has more tissue to keep running. Age carries a negative sign because BMR tends to drift down over the decades, largely tracking a slow loss of muscle mass if it isn't actively maintained. The two different constants for men and women reflect an average difference in typical lean-mass-to-fat ratio at a given weight — not a judgment about anyone's health, just what the data averages out to.

1. Start with your age, weight, height, and sex: 30 years, 70 kg, 170 cm.
2. Apply the Mifflin-St Jeor formula for men: 10 × 70 + 6.25 × 170 − 5 × 30 + 5 ≈ 1618 kcal/day.
3. Pick the activity multiplier that matches your typical week — moderately active (1.55×) is a common default.
4. Multiply BMR by that multiplier: 1618 × 1.55 ≈ 2507 kcal/day estimated maintenance calories (TDEE).
5. Decide a goal — subtract a moderate deficit to lose weight (commonly 10-20% of TDEE), add a similar surplus to gain, or stay close to TDEE to maintain.
6. Track actual weight over 2-4 weeks and compare against what you'd expect — adjust the number based on what really happens, not on the formula alone.

BMR alone is just the resting cost. Multiplying by an activity factor folds in movement, exercise, and the rest of daily life:

Office workers who train a few evenings a week often round themselves up to "very active" because the workout itself feels significant — but the other sixteen-odd waking hours spent mostly seated pull the honest weekly average back down. If you're unsure which row fits, the more conservative (lower) multiplier is the safer starting guess; you'll find out within a few weeks from your actual weight trend whether it needs nudging up.

Mifflin-St Jeor is the formula used above. Two others you'll run into elsewhere:

• Harris-Benedict (revised 1984): the older of the two, and research generally finds it overestimates BMR slightly against modern measurement, more so at higher body fat percentages.
• Katch-McArdle: uses lean body mass instead of total weight, which can be more accurate if you already know your body fat percentage precisely — say, from a DEXA scan — but isn't practical as a quick estimate for most people since it needs a measurement they don't have on hand.

Unless you have a specific reason to prefer one of the others — a known lean body mass figure, mainly — Mifflin-St Jeor's balance of simplicity and accuracy is why it's the default here and in most modern calculators.

Once you have a maintenance number, a deficit drives weight loss and a surplus drives weight gain. Using the moderately active TDEE of 2507 kcal/day as the base:

Using the rough approximation that 1 kg of body fat corresponds to about 7,700 kcal, a daily deficit of roughly 550 kcal targets about 0.5 kg of fat loss per week — a pace that's generally easier to sustain and less likely to cost you muscle than an aggressive crash deficit.

Protein does disproportionate work during a deficit — it helps preserve muscle and keeps you fuller for longer. A commonly cited range for active adults is 1.6-2.2 g per kg of body weight. At 70 kg, that's about 112-154 g of protein a day, or roughly 448-616 kcal from protein alone. Everything left over splits between carbohydrate and fat.

An illustrative split at the maintenance target of 2507 kcal/day, using a common ~30% fat share:

Treat that carb/fat split as a starting sketch, not a rule — endurance athletes typically want more carbohydrate, some people on lower-carb approaches shift the balance toward fat, and reasonable people disagree on the ideal ratio for general health. The protein number and total calorie target matter far more than getting the carb-to-fat ratio exactly right. If you want an actual body-fat reading before locking in a split, the body fat calculator is a reasonable next stop.

• Treating the estimate as exact. Formula output carries real uncertainty — let your weight trend over 2-4 weeks correct the number, not the other way round.
• Underestimating oil, sauces, and drinks. These are the easiest calories to miss; weighing food for a couple of weeks builds a surprisingly durable sense of portion size.
• Double-counting exercise. A tracker's workout estimate is already baked into an active TDEE multiplier — adding it again on top routinely leads to eating back more than you earned.
• Choosing too large a deficit. Aggressive cuts are hard to sustain and tend to cost muscle, energy, and eventually willpower — moderate and steady usually wins.
• Reacting to a single morning's number. Sodium, water, hormones, and digestion can swing the scale by a kilogram or more overnight with no fat change involved — go by the weekly average.
• Never recalculating. BMR shifts as weight changes, so a number set three months ago may no longer fit; revisit it periodically rather than anchoring to one static figure indefinitely.

None of this requires logging every gram forever — plenty of people track closely for a few weeks to calibrate their sense of portions, then relax into estimates once the numbers feel automatic. Whichever method you land on, the one that gets sustained for months beats the one that's precise for a week.

An estimated 1618 kcal/day BMR and about 2507 kcal/day maintenance calories (at moderate activity) is a solid starting point, not a prescription. Use it to set a deficit or surplus, keep protein in the 112-154 g range, and check in every few weeks against your actual weight trend rather than trusting the formula in isolation — that's the single habit that matters more than getting any one number perfectly precise. For medical conditions, pregnancy, or serious performance training, bring in a registered dietitian or doctor.

Figures are computed live from the age, weight, height, and sex you entered (or illustrative defaults), using the Mifflin-St Jeor BMR formula and standard activity multipliers. Deficit/surplus targets use the common approximation of 7,700 kcal per kilogram of body fat. Every formula-based estimate like this carries roughly 10% uncertainty even under ideal conditions, since it can't see your actual muscle mass, hormones, sleep, or day-to-day movement outside deliberate exercise. Nothing here is medical or nutrition therapy advice.