Calorie Calculator

What this calculator does

If you've ever opened a spreadsheet just to answer one health & fitness question, this calorie calculator replaces the whole workbook: type the numbers, read the result.

The Calorie Calculator estimates how many calories you should eat per day to lose, maintain or gain weight. It uses the Mifflin-St Jeor equation — the formula clinicians and dietitians consider the most accurate for healthy adults — to calculate your Basal Metabolic Rate, multiplies it by an activity factor to get your Total Daily Energy Expenditure (TDEE), then applies your weight goal as a calorie deficit or surplus.

Common mistakes

• Overestimating activity level — most desk workers who train 3–4×/week are 'lightly' to 'moderately' active, not 'very active'.
• Eating below your BMR — sustained under-eating slows metabolism, causes muscle loss and rebound weight gain.
• Not tracking accurately — hand-measured portions typically underestimate intake by 20–40%.
• Setting the deficit too aggressive — deficits larger than 1 kg/week are rarely sustainable outside medical supervision.
• Ignoring protein — inadequate protein during a deficit means you lose muscle along with fat.

When to use it

Use this calculator when starting a diet, cutting for a physique goal, gaining lean mass, tracking macros, planning meal prep, or resetting your intake after a plateau. Recalculate every 4–6 weeks or after any 3–5 kg change in body weight — your TDEE drops as you lose weight.

Pro tips for the Calorie Calculator

• Bookmark this page: the URL and inputs are all you need to reproduce the exact result later.
• Save your favorite scenarios by clicking the star icon — they're stored locally, no account needed.
• For big decisions, run best-case, expected, and worst-case scenarios and compare the breakdowns side by side.

Frequently asked questions

›Which formula does this use?

The Mifflin-St Jeor equation (1990), which studies consistently show is the most accurate BMR predictor for non-obese and obese adults compared to Harris-Benedict, Katch-McArdle and Owen.

›How many calories should I eat to lose weight?

A moderate deficit of 300–500 kcal below your TDEE produces roughly 0.3–0.5 kg (0.7–1 lb) of fat loss per week and is sustainable long-term. Larger deficits are only appropriate short-term or for people with significant excess body fat.

›How is TDEE different from BMR?

BMR is what you'd burn lying in bed all day — just organ function, breathing and body temperature. TDEE adds calories burned from movement, exercise, digestion (TEF) and non-exercise activity (NEAT). TDEE = BMR × activity factor.

›What activity level should I pick?

Sedentary = desk job, no exercise. Lightly active = 1–3 easy workouts/week. Moderately active = 3–5 workouts/week or a physical job. Very active = daily hard training. Athlete = twice-daily training. Most people overestimate — when in doubt, pick one level lower.

›Why do I need protein and macros too?

Total calories drive weight change, but macronutrients drive body composition. During a deficit, 1.6–2.2 g protein per kg of body weight preserves muscle. This calculator suggests ~2 g/kg protein, 25% of calories from fat, and the rest from carbs — a solid default for most goals.

›Can I eat below my BMR?

Not sustainably. Very-low-calorie diets are only appropriate short-term and typically under medical supervision. They increase muscle loss, hormone disruption, hunger, and the likelihood of regaining weight.

›How accurate is this calculator?

Mifflin-St Jeor is accurate to within about ±10% for most adults. For a personal number, weigh yourself daily for 2 weeks while tracking intake — your true maintenance is the intake at which weight is stable.

›Why did my weight loss stall?

As you lose weight, both BMR and the calorie cost of movement drop. Recalculate your TDEE using your new bodyweight, and reduce the deficit modestly rather than slashing calories further. Muscle-preserving strength training and adequate protein help.

›Does age affect calorie needs?

Yes. BMR falls roughly 5 kcal/day per year of age in the equation, mostly because lean mass declines with age. Staying active and strength-training can offset most of that decline.

›Kilojoules vs calories?

1 kcal = 4.184 kJ. Australian and European labels often use kJ; multiply kcal by 4.184 to convert.

›Can I embed the Calorie Calculator on my site?

Embedding isn't public yet, but you can link directly to this page — the URL is stable and shareable.

›Is the Calorie Calculator free to use?

Yes. Every calculator on CalcPilot, including the Calorie Calculator, is free with no sign-up, no watermark, and no export limit.

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