How many calories you need: a three-step calculation

Nobody can tell you an exact number off the top of their head. There is a good estimate, and then adjustment based on what the scale does over two weeks.

Step 1: basal expenditure

The Mifflin-St Jeor formula (the most accurate for most people):

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

Example: a man, 85 kg, 180 cm, 35 years → 850 + 1125 − 175 + 5 = 1805 kcal.

Step 2: multiply by activity

• Desk job, no training — × 1.2
• Training 1–3× a week — × 1.375
• Training 3–5× — × 1.55
• Training 6–7× or physical job — × 1.7

Our example with three sessions: 1805 × 1.55 ≈ 2800 kcal a day for maintenance.

Step 3: your goal

• Fat loss: −15 to −20 % → 2250–2400 kcal
• Maintenance: 2800
• Muscle gain: +10 % → 3100 kcal

Why apps miss

• Watches and treadmills overestimate session burn by 20–30 %.
• The formula does not know your muscle mass (more muscle, higher burn).
• People underestimate their food intake by 20–40 % when not measuring.

So the number is only a starting point — the truth is what the scale does over 2–3 weeks.

Adjusting

Weigh yourself every morning and watch the weekly average. If the average is flat and the goal is fat loss, cut 150–200 kcal. If you are losing more than 1 % of body weight per week, add 150 kcal.

The short version

• Formula → activity factor → goal.
• The number is an estimate; the scale is the truth.
• Adjust by the weekly average, not a single day.