How Many Calories Should I Eat? TDEE, BMR, and Deficits Explained

Published 2026-05-26 · By the CalculatorHive editorial team

"How many calories should I eat?" has a real answer, but it is an estimated range rather than a single number, and it comes from a short chain of arithmetic anyone can follow. This guide walks through that chain: resting metabolic rate, the activity multiplier that turns it into total daily expenditure, how large a deficit or surplus to apply, and where protein fits. Everything here is general information for healthy adults. Calorie targets are genuinely medical territory if you are pregnant or breastfeeding, under 18, over 65, managing diabetes, kidney disease, an eating disorder, or taking medication that affects appetite or metabolism — in those cases, get a target from a doctor or a registered dietitian rather than from any calculator, including ours.

What is the difference between BMR and TDEE?

Basal metabolic rate (BMR) is the energy your body uses lying still, awake, fasted, in a thermally neutral room — the cost of keeping your heart beating, your brain running, your kidneys filtering and your cells maintained. For most adults it is the largest single component of daily energy use, typically somewhere around 60–70% of the total for a sedentary person.

Total daily energy expenditure (TDEE) is everything: BMR, plus the thermic effect of food (roughly 10% of intake, spent digesting and absorbing it), plus deliberate exercise, plus non-exercise activity thermogenesis — fidgeting, standing, walking to the kitchen, gesturing while you talk. That last component varies enormously between people and is the main reason two individuals of identical size can have expenditures hundreds of calories apart.

You eat against TDEE, not BMR. Setting your intake at your BMR is not a modest deficit; for most people it is a severe one.

How do you calculate BMR? The Mifflin-St Jeor equation

Several equations exist — Harris-Benedict, Katch-McArdle, Cunningham — but Mifflin-St Jeor, published in 1990, is the one most commonly recommended for adults when body fat percentage is unknown. It takes weight in kilograms, height in centimetres, and age in years:

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

If you know your body fat percentage reasonably well, the Katch-McArdle equation works from lean body mass instead and tends to fit unusually lean or unusually muscular people better, since it does not have to infer composition from height and weight.

A worked example, start to finish

Take a 32-year-old woman, 5'6" (167.6 cm), 165 lb (74.8 kg), who does three moderate gym sessions a week and otherwise has a desk job.

Step 1 — BMR. (10 × 74.8) + (6.25 × 167.6) − (5 × 32) − 161 = 748 + 1,047.5 − 160 − 161 = 1,474.5, or about 1,474 kcal/day.

Step 2 — activity multiplier. Three sessions a week is "lightly active", a factor of 1.375.

Step 3 — TDEE. 1,474 × 1.375 ≈ 2,027 kcal/day to maintain weight.

Step 4 — apply a goal. For gradual fat loss, subtract 500: about 1,527 kcal/day. For gradual muscle gain, add 250–350: about 2,280–2,380. To maintain, eat around 2,000.

Notice the spread in that table. The gap between "sedentary" and "very active" for the same person is over 750 kcal — larger than most people's entire deficit. Choosing the multiplier honestly matters more than choosing the equation. Most people overestimate; if you are unsure between two levels, take the lower one and adjust from real-world results. The TDEE calculator runs all five levels at once so you can see the range, and the BMR calculator shows the resting figure on its own.

What does a sustainable deficit look like?

The familiar rule is that a pound of body fat holds about 3,500 kcal, so a 500 kcal daily deficit should produce a pound a week. It is a useful starting heuristic and a poor long-run predictor.

The reason is that expenditure is not a constant. As you lose mass, there is simply less of you to maintain and less to carry around, so both BMR and the energy cost of movement fall. A deficit that was 500 kcal against your starting TDEE is a smaller deficit against your TDEE twenty pounds later, and weight loss decelerates toward a new plateau. Researchers at the US National Institutes of Health made this point forcefully in modelling work published in The Lancet in 2011, proposing a more realistic rule of thumb: a sustained change of about 10 kcal per day eventually produces roughly 1 lb of weight change, with about half of that change realised within a year and most of it within three. Applied to a 500 kcal deficit, that implies an eventual plateau tens of pounds down but a first-year loss substantially below what the 3,500-calorie rule predicts.

The practical takeaways are unglamorous but useful. Expect the first weeks to move fastest, partly from glycogen and associated water. Expect the rate to slow, and treat that as physiology rather than failure. Recalculate your target after every 10–15 lb of change. And judge progress on a multi-week trend, not day-to-day scale readings, which swing by several pounds on sodium, carbohydrate intake, hydration and menstrual cycle phase.

Common deficit sizes, applied to the 2,027 kcal TDEE above: 250 kcal (1,777) for a slow, easily sustained cut; 500 kcal (1,527) as the standard; 750 kcal (1,277) as aggressive and hard to hold. Deeper than 750–1,000 kcal, most people are simply not eating enough food to hit protein and micronutrient targets. The calorie calculator lays these options out side by side.

How much protein, and what about the rest?

Protein does two things that matter in a deficit: it helps preserve lean mass while you lose fat, and it is the most satiating of the three macronutrients per calorie. The general adult reference intake — 0.8 g per kg — is a minimum for avoiding deficiency, not an optimum for someone dieting or training. Sports nutrition guidance for active people in an energy deficit typically lands around 1.6–2.2 g per kg of body weight.

For our 74.8 kg example, that is roughly 120–165 g of protein per day. At 4 kcal per gram, 140 g of protein is 560 kcal — over a third of a 1,527 kcal target, which is exactly why very low calorie intakes make adequate protein so difficult. If you are carrying a lot of excess weight, calculating from a target or lean body weight rather than current weight gives a more sensible figure; the protein calculator handles that.

Beyond protein, the split between fat and carbohydrate is largely a matter of preference and adherence, with a floor on fat (commonly 0.5–0.8 g per kg, to support hormone production and fat-soluble vitamin absorption) and enough carbohydrate to fuel whatever training you do. The macro calculator converts a calorie target into grams for whichever split you choose. The best split, in practice, is the one you can follow on a Wednesday evening in month four.

Why do very low intakes backfire?

Cutting harder does not linearly produce faster results, and below a certain point it works against you. Extremely low intakes make it near-impossible to hit protein and micronutrient targets from food, which accelerates loss of lean mass — and lean mass is metabolically active tissue, so losing it lowers your expenditure further. Hunger, fatigue, poor sleep, low training quality and irritability all scale with the size of the deficit, and each one erodes adherence. Prolonged severe restriction also carries real clinical risks, including gallstones and electrolyte disturbance, and can trigger or worsen disordered eating patterns.

As a general guide, intakes below roughly 1,200 kcal/day for women or 1,500 kcal/day for men are not recommended without medical supervision. Very low calorie diets do have a legitimate clinical role in specific circumstances, but they are prescribed and monitored, not self-selected. If your calculated deficit target falls below those thresholds, the answer is a smaller deficit over a longer period, or a conversation with a professional — not a smaller number.

Common questions

Should I eat back the calories my watch says I burned?

Usually not in full. Wearable estimates of exercise energy expenditure are frequently optimistic, and if you already chose an activity multiplier that reflects your training, adding exercise calories on top double-counts them. A common approach is to pick the multiplier that matches your typical week, eat that target consistently, and not adjust day to day. If you do eat back exercise calories, eating back half is a reasonable hedge against the error.

Why has my weight loss stalled at the same intake?

Three explanations cover most cases, often together: your expenditure genuinely fell as you got lighter, so the same intake is now a smaller deficit; portion sizes have crept up, since self-reported intake drifts over time even for careful trackers; and water retention is masking real fat loss on the scale. Recalculate your TDEE at your current weight, weigh food for a week to recalibrate, and compare four-week averages rather than daily readings.

Do calories from different foods count the same?

For energy balance, close enough — but not identically. Protein has a substantially higher thermic effect than carbohydrate or fat, so more of its energy is spent on digestion. Whole foods high in fibre are less completely absorbed than refined ones. And far more importantly, different foods differ hugely in how full they leave you per calorie, which drives whether you actually stick to the target. The label number is a good accounting tool and a poor description of what a food does to your appetite.

How long should I stay in a deficit?

There is no fixed limit, but many practitioners suggest running a deficit in blocks of roughly 8–16 weeks with planned periods at maintenance in between, particularly for people who train. Maintenance breaks give appetite regulation, training quality and adherence a chance to recover, and they rehearse the skill you will need permanently once you reach your goal. Regaining the ability to eat at maintenance without anxiety is part of the process, not a failure of it.