"Eat less, move more" is the most repeated weight loss advice of the last 50 years. It is also useless. Without a number, "less" is meaningless: one person's "less" is another person's maintenance. The actual question every weight loss plan has to answer first is: *how many calories should I be eating, specifically?*
This guide walks through the math. You will leave with your own personalized daily calorie target, a realistic weekly weight loss estimate, and a tracking workflow that actually survives the first month.
The Two Numbers That Matter: BMR and TDEE
Every calorie calculation starts with two numbers.
BMR (Basal Metabolic Rate) is what your body burns just staying alive: breathing, pumping blood, keeping your brain running, maintaining body temperature. If you lay in bed unconscious for 24 hours, you would still burn your BMR.
TDEE (Total Daily Energy Expenditure) is BMR plus everything else: walking to the kitchen, typing, digesting food, fidgeting, exercising. It is your *real* daily calorie burn.
You lose weight when you eat below your TDEE. You gain weight when you eat above it. There are no exceptions to this in healthy people. Metabolism differences between individuals are real but much smaller than most internet claims suggest, usually ±10% of the calculated TDEE.
The Mifflin-St Jeor Formula (The One That Actually Works)
Most TDEE calculators use the Mifflin-St Jeor equation. Published in 1990, it remains the most accurate BMR formula for the general population: more accurate than the older Harris-Benedict formula that many apps still use.
For men:
BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
For women:
BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
Example: A 35-year-old man, 180 cm tall, weighing 85 kg.
BMR = (10 × 85) + (6.25 × 180) − (5 × 35) + 5
BMR = 850 + 1125 − 175 + 5 = **1805 calories/day**
That is what he burns laying still for 24 hours. Now multiply by an activity factor to get TDEE.
Activity Multipliers
| Activity Level | Multiplier | Description |
|---|---|---|
| Sedentary | 1.2 | Desk job, little or no exercise |
| Lightly active | 1.375 | Light exercise 1-3 days/week |
| Moderately active | 1.55 | Moderate exercise 3-5 days/week |
| Very active | 1.725 | Hard exercise 6-7 days/week |
| Extremely active | 1.9 | Physical job + hard daily training |
Most people overestimate their activity level. If you go to the gym 3x a week but sit at a desk all day, you are "lightly active" at best. Be honest: overestimating is why calorie deficits fail.
Our example man, desk job + 3 gym sessions = lightly active (1.375).
TDEE = 1805 × 1.375 ≈ **2482 calories/day**
The Deficit: How to Turn TDEE Into a Weight Loss Target
1 pound of body fat contains roughly 3,500 calories. A 500 cal/day deficit produces ~1 lb of fat loss per week. A 1,000 cal/day deficit produces ~2 lbs, but becomes unsustainable for most people within 3-4 weeks.
Recommended deficits:
| Goal | Deficit Below TDEE | Expected Weekly Loss |
|---|---|---|
| Slow and sustainable | 250-400 cal | 0.5-0.8 lb |
| Moderate | 400-600 cal | 0.8-1.3 lb |
| Aggressive (short-term) | 700-1000 cal | 1.5-2 lb |
| Unsustainable | 1000+ cal | Often leads to bingeing |
For our example:
- TDEE: 2482 cal
- Moderate deficit target: 1900-2050 cal/day
- Expected loss: about 1 lb per week
This is the real number. No fad diet, no "metabolism booster," no "toxin cleanse" changes this math. If stubborn belly fat is the specific goal, our 90-day science-based belly fat plan builds a complete program around exactly this deficit.
Protein: The Non-Negotiable
Calories determine whether you lose weight. Protein determines whether you lose *fat* or *muscle*. In a deficit, aim for:
- 0.7-0.8g per pound of bodyweight for general fat loss
- 0.9-1.0g per pound if you are lifting weights and want to preserve/build muscle
For an 85 kg (187 lb) person: 130-190g protein per day.
This is higher than most people eat. Tracking protein is where most fat loss plans quietly fail: people hit the calorie number but eat 60g protein and lose muscle along with fat. Photo calorie counters make this easy because macros show on every logged meal.
The Tracking Problem (And Why Most People Quit by Week 3)
Here is the inconvenient truth: accurate tracking is hard. Research repeatedly shows people underestimate their intake by 20-40% when self-reporting. The "I ate around 1800 calories today" gut estimate is almost always wrong.
The old solution was logging every meal into a database manually: accurate but so tedious that adherence falls off within 2-3 weeks for most users.
The 2026 solution is photo-based AI calorie counting. Apps like Calow identify food from a photo, estimate portions, and log the totals in seconds. No searching, no typing, no forgetting the cooking oil.
What good tracking looks like:
- Every meal photo-logged within 10 minutes of eating (memory decays fast)
- Drinks counted: lattes, juice, soda, alcohol all matter
- Cooking oil estimated when eating out (add 100-200 cal to restaurant meals)
- Weekends tracked the same as weekdays (weekends are usually where deficits break)
How to Use Your TDEE Number Day-to-Day
Week 1-2: Eat at your calculated target. Do not panic if weight swings 2-3 lbs, that is water. Track everything.
Week 3: Calculate a 7-day average weight. Compare to week 1 average. If down 1-2 lbs, stay the course. If flat, tighten tracking before reducing calories: you are almost certainly eating more than you think.
Week 4 onward: Re-check weekly. Every 10-15 lbs lost, recalculate TDEE (lighter body = lower BMR). The deficit that worked at 200 lbs will stall you at 180 lbs.
Common Calorie Calculation Mistakes
Using the wrong activity multiplier. Sedentary means sedentary. Lifting 3x a week with a desk job is "lightly active," not "very active."
Forgetting that TDEE drops as you lose weight. Your maintenance calories at goal weight might be 500 below your maintenance calories today.
Eyeballing portions. A "tablespoon" of peanut butter is almost always 2 tablespoons. A "handful" of nuts is usually 2 handfuls. Photo logging bypasses this entirely.
Not accounting for weekends. Five perfect weekdays and two "casual" weekends often net a surplus, not a deficit.
Chasing a "fast metabolism." Your metabolism is fine. The issue is almost always intake accuracy.
Cutting too aggressively. A 1200-calorie target for a 200-pound person will work for 10 days and then crash into a binge. Sustainable beats fast. If hitting the target feels like a constant fight, an eating structure like 16:8 intermittent fasting makes the same deficit easier to hold.
Calculate Yours in 2 Minutes
Step 1: Plug your stats into the Mifflin-St Jeor formula above.
Step 2: Multiply by your honest activity level.
Step 3: Subtract 300-500 for a sustainable fat loss target.
Step 4: Calculate your protein target (0.8g per pound).
Step 5: Start tracking every meal: Calow handles the logging automatically through photos.
The Verdict
TDEE math is not magic, it is arithmetic. Once you know your number, weight loss stops being a mystery and becomes a tracking problem. And tracking is exactly the problem AI calorie counters solved.
If you have calculated your TDEE before but never stuck with tracking, the friction was the issue, not your willpower. Try a photo-based calorie counter for two weeks and see if it changes the equation. Calow is free to download and the entire logging workflow takes under 2 minutes a day.