How to use the Calorie Calculator
- Enter age, sex, height and weight.
- Pick the activity level that reflects a typical week.
- Choose your goal and the rate of change you want.
- Weigh yourself at the same time of day for two weeks before adjusting the target.
How the calculation works
The calculation starts from a Mifflin-St Jeor resting rate, scales it by activity to get maintenance, then applies a goal adjustment. The conventional conversion is that roughly 7,700 calories equate to a kilogram of body mass, so a 500-calorie daily deficit predicts around half a kilogram of loss per week.
That conversion is a simplification. Early weight change is dominated by glycogen and water, plateaus are normal, and long deficits reduce both resting rate and spontaneous activity. The honest use of a calorie target is as a hypothesis: hold it steady for two to three weeks, look at the trend rather than daily readings, and adjust by 100 to 200 calories.
Target = BMR × activity factor ± goal adjustment (≈500 kcal/day per 0.45 kg per week)Source: Mifflin-St Jeor BMR with FAO/WHO/UNU activity multipliers; 7,700 kcal per kg energy-density convention.
Worked example
A 41-year-old woman, 161 cm, 74 kg, moderately active, aiming to lose 0.5 kg per week.
- BMR = 10(74) + 6.25(161) − 5(41) − 161 = 740 + 1,006 − 205 − 161 = 1,380.
- Maintenance = 1,380 × 1.55 = 2,139.
- Deficit for 0.5 kg/week ≈ 550 calories.
Target ≈ 1,590 calories per day, with maintenance at about 2,140 once she reaches her goal weight.
Frequently asked questions
Is there a minimum intake I should not go below?+
Very low intakes make adequate protein and micronutrients hard to reach and are often clinically supervised for that reason. Around 1,200 for women and 1,500 for men are commonly cited floors — below that, seek professional guidance.
Why did I gain weight the week I started eating better?+
More fibre, more carbohydrate and higher sodium all increase water retention and gut content. Scale weight can rise for a week or two while fat is genuinely being lost; the trend over a month is what matters.
Do I need to count calories forever?+
No. Most people track for a period to calibrate portion sizes, then move to habits — protein at each meal, consistent meal structure — and return to tracking only when progress stalls.
Does meal timing change the calorie requirement?+
Total intake drives weight change. Timing affects training performance, hunger and sleep, all of which influence adherence, but it does not change the arithmetic of the target.
Last reviewed August 31, 2026. We review this page whenever the underlying formula, tax year, published rate or standard changes.