How many calories should I eat a day?

Short answer: most women need somewhere between 1,600 and 2,400 calories a day, and most men between 2,000 and 3,000. That’s the range in the US Dietary Guidelines.

That’s a wide range. Where you land depends on your size, your age and how much you move. Here’s how your own number is worked out, then a calculator to get it.

Where your calories go

Your body spends energy in three ways:

• Staying alive. Breathing, your heartbeat, your brain, keeping warm. This is the biggest part by far, most of what you burn in a day, even if you never leave the sofa.
• Digesting food. A small slice. Protein costs the most to digest, fat the least.
• Moving. Workouts, but also everything else: walking to the shop, taking the stairs, fidgeting, chores. For someone at a desk all day that’s a small share. For a very active person it can be a big one.

That everyday movement is the part that changes most between people. Two people of the same size can burn very different amounts just from how much they move around outside the gym.

Age plays a part too. After about 25, your resting burn drops by a few percent each decade, mostly because people lose muscle. Keeping your muscle slows that down.

What are maintenance calories?

Your maintenance calories are what you burn in a normal day, all three parts added up. Eat that much and your weight stays about the same. Eat less and you lose, eat more and you gain. Every target starts from this number.

How your number is worked out

1. What you burn at rest. The calculator uses the Mifflin–St Jeor equation (1990). A review of the common formulas (Frankenfield et al., 2005) found it the most reliable: for most people, it lands within 10% of what a lab would measure.

2. Times how much you move. Your resting number gets multiplied by your activity level. That gives your maintenance calories: what you can eat without gaining or losing.

Most people overestimate this. If you’re not sure, pick the lower one.

3. Then your goal. To lose weight, eat about 20% less than your maintenance, never more than 500 calories a day under it. To gain, eat about 350 more. To keep your weight, eat your maintenance.

The calculator also has its own page. Bookmark it and work your number out again as your weight changes.

How many calories to lose weight

Eat about 20% under your maintenance. In plain terms, that’s roughly four-fifths of what you eat now. It’s enough to lose weight at a steady pace without feeling starved.

Why a percentage and not a fixed number? Because 500 calories is a gentle cut for a tall, active man and a harsh one for a small woman. Twenty percent scales with you. The 500 cap keeps bigger people from cutting too hard too.

Expect the first weeks to move faster than the later ones. When you eat less for a while, your body adapts: it burns a little less at rest, you move a little less without noticing, and a lighter body needs less anyway. Research on this (Hall et al., 2011) shows the old “3,500 calories = 1 pound” rule overestimates weight loss over months. Slowing down is normal. It doesn’t mean it stopped working.

Why eating too little backfires

A bigger cut sounds faster. It usually isn’t.

Eat too little for too long and your body treats it like a food shortage. Your metabolism slows down to match. You get tired, foggy and irritable, you sleep worse, and you recover badly from exercise. In women, periods can become irregular or stop. And you’re much hungrier, which is why crash diets end in a binge.

That’s why the calculator never goes below 1,200 calories a day. Going lower is something to do with a doctor, not an app.

How many calories to gain weight

Add about 350 to your maintenance. Keep it small: if you train, most of what you gain will be muscle. A big surplus mostly adds fat.

Protein, carbs and fat

Calories are the total. Where they come from matters too, so the calculator splits them up:

• Protein: 2 g per kg of body weight. Protein keeps you full the longest and protects your muscle when you eat less. How much you need depends on you: about 0.8 to 1.2 g per kg if you don’t move much, 1.6 to 2.2 g if you’re active, and more when you’re trying to lose fat or build muscle. 2 g sits in the middle of the active range.
• Fat: a quarter of your calories. Your body needs fat for hormones and to absorb some vitamins. Don’t go much lower.
• Carbs: the rest. They’re your main fuel, especially if you train.

Is that much protein bad for your kidneys?

Not if your kidneys are healthy. Reviews of the research (Devries et al., 2018) find no difference in kidney function between people eating more protein and people eating less. In one year-long study (Antonio et al., 2016), trained men spent months eating over 3 g per kg a day, with no harm to their kidneys or liver. Protein is also very filling, so it’s hard to overdo by accident.

The exception: if you have kidney disease, or a condition like PKU, you may need less protein, not more. Ask your doctor for your number.

It’s a starting point

Every formula is an estimate. So use your number for two or three weeks and watch your weight. Weigh yourself on a few mornings and look at the trend, not one day. Weight moves up and down with water, salt and sleep.

• Losing about as fast as you wanted? Keep going.
• Not moving after three weeks? Take off 100 to 200 calories.
• Losing much faster, or always hungry and tired? Add 100 to 200.

Work it out again every time you lose 5 kg (about 10 pounds). A lighter body needs a little less.

Who shouldn’t use a calculator

If you’re pregnant or breastfeeding, under 18, managing a health condition, or have a history of eating disorders, talk to your doctor or a dietitian. They’ll give you a number that fits you.

Counting is the hard part

Knowing your number takes a minute. Eating to it every day is where most people give up: the searching, the weighing, the logging.

That’s what Fabee is for. It sets your target when you start. Then you just tell it what you ate, like a text to a friend, and it counts every meal against your number.