How many calories do you need in a day?
What your body uses each day, and what to eat to lose weight at the rate you choose. The slider stays within clinical guidance.
2,202 kilocalories a day. Eat this and your weight holds where it is.
That is a daily deficit of 551 kilocalories.
This is a calculator, not advice. Agree your target and rate with your doctor.
Eat this to lose 0.5kg a week
1,651 kilocalories a day, from where you are now.
And this once you reach 81kg
1,527 kilocalories a day, to still be losing 0.5kg a week at that weight.
Why the second figure is lower
How this works
Why you need less as you get lighter
A smaller body uses less energy. On your figures, maintenance falls by about 14 kilocalories a day per kilogram lost, roughly 87 per stone. By your target, that’s about 124 kilocalories a day less.
So the gap you start with shrinks as you lose weight. Where the two lines meet, weight stops changing.
If unsure about your activity level, choose the lower one and check against your scales over a few weeks.
The 3,500 calorie rule
A pound of body fat stores about 3,500 kilocalories, so a daily gap of 500 is roughly a pound a week. The tool uses this to turn your chosen rate into calories.
It’s an estimate. Reasonable calculations range from about 3,450 to 3,850.
You also lose some lean tissue, which stores less energy, so real results vary.
Why the first few weeks look different
Early weight loss is mostly water, from stored carbohydrate (glycogen). It can be around 2kg and isn’t fat.
Glycogen holds at least 3g of water per gram (Murray and Rosenbloom, Nutrition Reviews, 2018).
On identical calories, a low-carbohydrate diet lost more early weight, mostly water (Yang and Van Itallie, J Clin Invest, 1976).
Judge the trend from about week four. A normal weekend can put 1 to 2kg of water back, not fat.
Why weight loss slows
Three things: a smaller body needs less energy, the body adapts a little further, and appetite returns so intake drifts up.
Appetite has the biggest effect in practice (Thomas and colleagues, Am J Clin Nutr, 2014).
Plateaus come later when appetite is treated directly (Hall, Obesity, 2024). How treatment works.
Sources and limits
Your maintenance. Mifflin–St Jeor equation (Am J Clin Nutr, 1990) with standard activity multipliers.
The limits on the slider. The tool stops at whichever of these you reach first:
- A 600 kilocalorie daily deficit. NICE CG189, recommendation 1.7.5.
- 0.5 to 1kg a week. NICE’s recommended rate range.
- 1% of your body weight a week. Garthe and colleagues, Int J Sport Nutr Exerc Metab, 2011.
- At least 1,200 kilocalories a day. Sievenpiper and colleagues, Obesity Pillars, 2025.
Never below 800 kilocalories a day. NICE advises very low calorie diets only with clinical supervision (CG189 1.7.7–1.7.9).
Other sources. Wishnofsky, Am J Clin Nutr, 1958; Yang and Van Itallie, 1976; Murray and Rosenbloom, 2018; Thomas and colleagues, 2014; Hall, 2024.
These are estimates. Real maintenance can differ by several hundred kilocalories a day. Check against your scales over a few weeks. For a detailed forecast, try the NIH Body Weight Planner.
General information about energy balance, not medical advice. It knows nothing about you beyond the figures you typed and it is not a prediction of what any treatment will do. If you are making decisions about how much you eat, do it with a clinician who knows your history.