How Many Calories Should You Eat a Day? The Honest Math
The generic answer — 2,000 for women, 2,500 for men — is a labeling convention, not advice. Your actual number depends on your body size, age, and how much you move. Here's how to find it in five minutes.
Step 1: Estimate Your BMR
Your Basal Metabolic Rate is what your body burns doing nothing — keeping organs running, maintaining temperature, repairing tissue. The Mifflin-St Jeor equation is the most accurate common formula:
- Men: (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5
- Women: (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161
Example: a 35-year-old woman, 70 kg, 168 cm → 700 + 1,050 − 175 − 161 = 1,414 kcal BMR.
Step 2: Multiply by Activity
BMR is not your budget — you also move. Multiply by an activity factor:
| Lifestyle | Multiplier |
|---|---|
| Desk job, little exercise | 1.2 |
| Light exercise 1–3 days/week | 1.375 |
| Moderate exercise 3–5 days/week | 1.55 |
| Hard exercise 6–7 days/week | 1.725 |
Most people overestimate this — a desk job plus three gym sessions is "light to moderate," not "hard." Our example at 1.375 lands at ~1,945 kcal/day. That's her TDEE: eat that, weight stays put.
Step 3: Adjust for Your Goal
- Lose weight: subtract 300–500 kcal. A 500 kcal daily deficit ≈ 0.5 kg lost per week. Bigger deficits backfire — hunger wins eventually.
- Gain muscle: add 200–300 kcal with adequate protein (1.6–2.2 g per kg of body weight).
- Maintain: eat your TDEE and confirm with the scale over 2–3 weeks.
The Part Everyone Skips: Measurement Error
Here's the uncomfortable truth: your TDEE estimate can be off by ±10%, and self-reported food intake is typically under-counted by 20–40%. The formula isn't the hard part — knowing what you actually ate is.
That's why logging matters more than calculating. Track honestly for two weeks, watch the scale trend, and adjust: weight not moving on your "deficit"? Your real intake is higher than your log. Cut 200 more or log more accurately.
Not sure what your meals actually contain? Check our calorie chart for common foods — real serving sizes, not just per-100g numbers. Cross-checking a few staples like rice, chicken breast, and peanut butter usually reveals where the hidden calories live.
Make the Logging Part Take 3 Seconds
The math above takes five minutes once. Logging is what you do every day — and it's why most people quit tracking within two weeks.
NibbleCal removes that friction: snap a photo of your plate and the AI identifies the food, estimates portions, and logs calories and macros in about 3 seconds. No database searching, no portion guessing. Try it free — no account needed for your first estimate.