The honest answer is "it depends" — but you can calculate a solid starting point in about two minutes. Estimate your Basal Metabolic Rate (BMR) with the Mifflin-St Jeor equation, multiply by an activity factor to get your Total Daily Energy Expenditure (TDEE), then subtract 300–500 calories to lose weight or add 200–300 to gain lean muscle.
As a rough population average, adult women maintain weight on roughly 1,600–2,400 calories/day and adult men on roughly 2,000–3,000 calories/day. These are broad averages, not your number — individual metabolism varies widely.
The catch: the starting number is the easy part. Keeping it accurate over months — as your body adapts and your weight changes — is where most people fail. That is exactly the problem adaptive tracking solves.
"How many calories should I eat a day?" is one of the most searched nutrition questions, and almost every answer online gives you a single number as if it were a fact. The truth is more useful: you can compute a genuinely good starting estimate in two minutes with a well-validated formula, but that number is a starting point, not a permanent setting. This guide shows you exactly how to calculate it, walks through real worked examples, and — importantly — explains why your number stops working after a few weeks and what to do about it.
Your daily calorie target comes from three quick steps: estimate the energy your body burns at rest (BMR), scale it up for your activity level (TDEE), then adjust for your goal. Let us go through each.
Your Basal Metabolic Rate is the number of calories your body burns just to keep you alive at complete rest — breathing, circulating blood, maintaining body temperature. It is the single largest chunk of your daily energy use, typically 60 to 70 percent of the total.
The most widely used and reliable estimate is the Mifflin-St Jeor equation, which nutrition professionals generally consider the most accurate of the common formulas for the general population. It uses metric units (kilograms and centimetres):
Men: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5
Women: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161
Working in pounds and inches? Convert first: divide pounds by 2.205 to get kilograms, and multiply inches by 2.54 to get centimetres. Then use the formulas above.
The only difference between the two versions is the final constant (+5 for men, −161 for women), which reflects average differences in body composition. Enter your numbers and you have your BMR — the floor of your daily energy needs.
Nobody spends the whole day lying still. Your Total Daily Energy Expenditure (TDEE) is your BMR scaled up to account for movement: walking, working, exercising, even fidgeting. You estimate it by multiplying your BMR by an activity factor.
| Activity level | Typical week | Multiplier |
|---|---|---|
| Sedentary | Desk job, little or no exercise | × 1.2 |
| Lightly active | Light exercise 1–3 days/week | × 1.375 |
| Moderately active | Moderate exercise 3–5 days/week | × 1.55 |
| Very active | Hard exercise 6–7 days/week | × 1.725 |
| Extra active | Very hard training or a physical job | × 1.9 |
Most people overestimate here. Three gym sessions a week plus a desk job is "lightly" to "moderately" active, not "very active." When in doubt, pick the lower multiplier — it is easier to add calories later than to discover you have been overeating for a month.
Your TDEE is your maintenance level — the intake that keeps your weight roughly stable. From there you nudge up or down depending on what you want:
Do not go too low. As a general safety floor, most adults should not eat below roughly 1,200 calories/day for women or 1,500 calories/day for men without medical supervision. Very aggressive deficits accelerate muscle loss, deepen metabolic adaptation, and are hard to sustain. Slower is almost always better.
Formulas are abstract until you see them run. Here are three realistic profiles from start to finish.
Notice how different three "normal" people are: from about 1,525 to nearly 3,000 calories a day. This is exactly why a single number from a generic article is close to useless — your target depends on your body, your activity, and your goal.
Here is the part most calculators never mention. That tidy number you just computed is accurate on the day you compute it — and then it quietly drifts out of date. Three forces push it off:
When you eat in a deficit, your body defends itself. Non-exercise movement drops, hormones shift, and you burn fewer calories than the formula predicts — a well-documented effect called metabolic adaptation. Research suggests this adaptation can be meaningful over weeks of dieting, so the deficit you started with slowly shrinks even if your eating never changes.
BMR is tied directly to body weight in the Mifflin-St Jeor equation. Lose 5 kg and your maintenance level genuinely falls. The 1,525-calorie target that produced steady loss in week one can quietly become your maintenance level by week eight — and the scale stalls even though you are "doing everything the same."
Portion estimates creep. Untracked bites, oils, dressings, and "close enough" logs accumulate. Over a few weeks, a real 400-calorie deficit on paper can become a 100-calorie deficit in reality — barely enough to see on the scale.
The result is the classic plateau: you feel like you are following your target perfectly, yet progress stops. Static calculators cannot see any of this, because they hand you one number and walk away. We go deeper on this in why static calorie counters fail, and on the fix in our breakdown of the adaptive energy expenditure algorithm.
A good calorie target is not a one-time calculation — it is a moving target that needs to be recalibrated as your body changes. This is the core idea behind how PlateLens works:
A note on your health. These formulas and ranges are general educational guidance for healthy adults, not medical advice. If you are pregnant or breastfeeding, managing a medical condition, taking medication that affects weight, or have any history of disordered eating, talk to a doctor or registered dietitian before setting a calorie target or starting to track.
You can absolutely answer "how many calories should I eat a day" in two minutes: estimate your BMR with Mifflin-St Jeor, multiply by an honest activity factor, and adjust 300–500 down to lose or 200–300 up to gain. That gives you a genuinely good starting point — better than any generic number online.
Just remember that it is a starting point. Your body will adapt, your weight will change, and your logging will drift, so the number that works today will need adjusting in a few weeks. The people who succeed long term are not the ones who calculate the perfect number once — they are the ones who keep it accurate over time. That is the whole reason adaptive tracking exists.
PlateLens calculates your calorie and macro targets during setup, then keeps them honest as your body changes. Free plan never expires: 3 AI photo scans a day, unlimited manual and barcode logging, no credit card.
For most adults, 1,200 calories a day is the commonly cited lower bound for women eating without medical supervision, and roughly 1,500 for men. Going below those levels for long periods risks nutrient deficiencies, muscle loss, and metabolic adaptation, and should only be done under the guidance of a doctor or dietitian. Many people who land at 1,200 have simply set too aggressive a deficit — a smaller 300 to 500 calorie deficit is usually more sustainable and produces results you can actually keep.
It depends on how you calculated your target. If your activity multiplier already includes your training, exercise is baked into your TDEE and you should not add it back on top or you will double-count. If you used a sedentary multiplier and log workouts separately, eating back some of those calories makes sense. Pick one method, hold it steady for a few weeks, and let your real weight trend confirm whether the number is right.
A kilogram of body fat is commonly estimated to store around 7,700 calories, so losing 1 kg requires roughly a 7,700-calorie cumulative deficit. At a 500-calorie daily deficit that is about 15 days per kilogram, close to 0.5 kg per week. It is an approximation, not a precise law — early weight change also includes water and glycogen, which is why the scale rarely moves in a straight line.
Usually the deficit is smaller than it looks, or your maintenance level has fallen. Tracking drift, untracked bites, oils, and generous portion estimates quietly erase a deficit. As you lose weight your body also burns fewer calories, so a week-one target can become maintenance by week six through metabolic adaptation. Water retention can mask real fat loss for a week or two. Judge progress over three to four weeks, tighten your tracking accuracy, and recalculate your target as your weight changes.
A physically demanding job — construction, warehouse, nursing — pushes you toward the higher activity multipliers, typically 1.725 (very active) or 1.9 (extra active). Multiply your BMR by that figure rather than a sedentary 1.2. Because job intensity varies day to day, treat the result as a starting estimate and adjust based on your real weight trend over two to three weeks.
A good rule of thumb is to recalculate every time your weight changes by about 4 to 5 kg (roughly 10 lbs), or whenever progress stalls for more than two to three weeks. Your BMR is tied to your body weight, so a number calculated months ago will drift as your body changes. Adaptive trackers do this continuously in the background so you never have to redo the math by hand.