Diet calorie maths: how much should you eat to lose weight?

Turning a vague intention into a number you can check

"Eat a bit less and exercise more" is a resolution, not a plan. Once you know how much less, and roughly when that adds up to a given number of kilograms, you can actually build a schedule and review it. This article walks through that calculation step by step.

Step 1: 1kg of fat is about 7,700kcal

Losing 1kg of body fat requires roughly a 7,700kcal energy deficit. That figure is the starting point for almost every diet calculation.

Step 2: find your maintenance calories

A deficit needs a baseline. That baseline is your TDEE — basal metabolic rate multiplied by an activity factor. The method is covered in BMR and TDEE explained.

For a 30-year-old woman, 163cm, 58kg, exercising three to five times a week, maintenance is roughly 2,000kcal. Cutting 500 gives a target of 1,500kcal a day.

Step 3: pick a rate you can hold

It is tempting to make the deficit large. The commonly recommended pace, though, is 0.5–1% of body weight per week — for someone at 60kg, that is 0.3–0.6kg.

Go faster and a larger share of what you lose is muscle rather than fat. Less muscle means a lower metabolic rate, which means you now need less food than before just to maintain. That is the usual route to regaining everything afterwards.

Roughly 1,200kcal for women and 1,500kcal for men are treated as practical floors. If your target lands below that, adding activity is safer than removing more food.

Step 4: when the scale will not move

If two or three weeks pass with no change, it is usually one of these.

• The activity factor was too generous — the most common cause. Drop one level and recalculate.
• Something is missing from the log — syrup in coffee, oil used in cooking, a couple of bites while cooking. One tablespoon of cooking oil alone is about 120kcal.
• Portions were eyeballed — a bowl of rice can be 150g or 250g depending on who serves it. Using a scale for the first two weeks removes most of the error.
• Water is hiding the change — salty meals, menstrual cycles and hard training all swing weight by a kilo or two. Read weekly averages, not daily numbers.

Step 5: handling the plateau

As you get lighter, your maintenance calories fall with you. Maintenance at 70kg is not maintenance at 65kg. Keep using the original number and the deficit quietly disappears.

Recalculate every 3–5kg of change. Entering your new weight into the calculator on this site immediately gives an updated target.

Is total calories all that matters?

For weight on the scale, total intake is the dominant factor. But the same 1,500kcal behaves differently depending on what it is made of.

Enough protein limits muscle loss during a deficit and keeps you full for longer. Vegetables and whole grains bring fibre, so the same calories fill you up far more. Calories you drink, by contrast, barely register as fullness and quietly push the daily total up.

How to split things is covered in setting your carb, protein and fat split.

This article is general information and is not a substitute for medical advice. If you have a health condition, or are pregnant or breastfeeding, speak with a professional before changing your diet.