How many calories should you eat to lose weight?

Type “how many calories to lose weight” into any search bar and you’ll get a number. Usually 1,200 for women and 1,800 for men, presented as if it were a law of physics.

It isn’t. Those numbers came from generic dieting advice in the 1980s, and for a lot of people they’re either wildly too low or genuinely too high. A 1.55 m office worker and a 1.90 m construction worker do not have the same energy needs, and pretending otherwise is exactly why so many diets stall in week three.

So let’s do this properly. Not with a magic number, but with the actual arithmetic your body runs on.

First: what a calorie deficit actually is

Body weight change is governed by energy balance. Eat less energy than you spend and your body makes up the difference from stored energy — mostly fat, and some muscle if you’re careless about it.

That “spend” figure is your total daily energy expenditure (TDEE), and it’s made of four parts:

• Basal metabolic rate (BMR) — what you’d burn lying in bed all day. Typically 60–70% of the total.
• Activity — deliberate exercise. Usually far smaller than people assume.
• NEAT — fidgeting, walking to the shops, standing up. Surprisingly large and highly variable.
• Digestion — the energy cost of processing food itself, around 10%.

Step one: find your maintenance calories

Before you can subtract anything, you need to know what you’re subtracting from. The standard approach is the Mifflin-St Jeor equation, which the Academy of Nutrition and Dietetics has repeatedly found to be the most accurate of the common predictive formulas for healthy adults.

For men: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5

For women: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161

Then multiply by an activity factor between 1.2 (sedentary) and 1.9 (very active) to reach your TDEE.

If you’d rather not do this by hand, our daily calorie calculator runs the same equation and gives you a maintenance figure plus a macro split in about twenty seconds. We’ve written up exactly which formulas we use and why if you want to check our working.

Step two: choose a deficit you can actually sustain

Here’s where most advice goes wrong. Bigger deficit, faster results, right?

Only on paper. A very aggressive deficit brings muscle loss, relentless hunger and a diet you abandon. Guidance from bodies like the NHS and the CDC favours a gradual 0.5 to 1 kg per week.

In practice:

Deficit	Approx. weekly loss	Realistic for
10–15% below TDEE	0.25–0.5 kg	Long timelines, preserving muscle
20% below TDEE	0.5–0.75 kg	Most people, most of the time
25%+ below TDEE	1 kg+	Short, supervised phases only

A 20% deficit is the sensible default. If your TDEE is 2,400 kcal, that’s about 1,920 kcal per day — not 1,200.

Do not go below roughly 1,200 kcal (women) or 1,500 kcal (men) without medical supervision. Below that it becomes genuinely difficult to hit micronutrient requirements, and this is the point where a dietitian should be involved rather than an app.

Step three: protect your muscle while you lose fat

Losing weight and losing fat are not the same achievement. In a deficit without enough protein and without resistance training, a meaningful share of what you lose is lean tissue — which lowers your BMR and makes the whole thing harder later.

Two things prevent most of that:

1. Eat enough protein. Roughly 1.6–2.2 g per kg of bodyweight is the range that shows up repeatedly in the literature for people in a deficit. We go deeper on this in how much protein you actually need per day.
2. Lift something heavy twice a week. It signals to your body that the muscle is worth keeping.

This is also why tracking macros rather than just total calories matters. Two 1,900-calorie days can produce very different body composition outcomes.

Why the scale lies to you (and what to watch instead)

You cut calories, you’re consistent for five days, and the scale hasn’t moved. Or it’s gone up.

This is almost always water, not fat. Glycogen binds roughly 3 g of water per gram stored, so a high-carb meal, a hard workout, a salty dinner, or a poor night’s sleep can each swing the reading by a kilo or more — completely independently of your fat stores.

Fat loss is slow; water weight is fast. Weigh daily, use the weekly average, and give a trend two to three weeks. For a target-weight sanity check, the ideal weight range calculator is better than a number that merely sounded good.

What actually determines whether this works

A 15% deficit you follow for six months beats a 30% deficit you abandon in three weeks, every single time. Which means the practical question isn’t “what’s the optimal number” — it’s “what’s the largest deficit I can maintain without my life falling apart.”

The tracking side matters too, and it’s where the arithmetic quietly breaks down. Self-reported food intake is notoriously under-reported — studies on dietary recall have found gaps of 20% or more between what people report and what they actually eat. If you’re eating 20% more than you log, a 20% deficit is just maintenance with extra admin.

---

This article is general information, not medical advice. If you have a health condition, are pregnant, or are considering a substantial change to your diet, talk to a doctor or registered dietitian first.