How big should my calorie deficit be?

For most adults about 275 to 550 kcal a day below maintenance, roughly 0.25 to 0.5 kg (half a pound to a pound) a week.

Is a 500-calorie deficit enough to lose weight?

Yes, for most people. It is about a pound a week at first, and the pace slows later.

How many calories are in a pound of fat?

The old rule says about 3,500 kcal per pound, about 7,700 per kilo. It fits the first weeks, but it overstates how much you lose over a year.

Calorie deficit: how big it should be and how to work it out

A calorie deficit means you take in less energy than your body uses, so it makes up the difference from its stores. For most adults 275 to 550 kcal a day below maintenance is enough, roughly 0.25 to 0.5 kg (half a pound to a pound) a week. That is about two slices of bread and a can of beer, not half your food.

Keto, intermittent fasting and "nothing after 6 pm" work for fat loss when they create a deficit and don't when they don't. That's why I'd rather you understand the deficit than pick the "right" diet.

What is a calorie deficit?

A calorie deficit is the gap between the energy your body uses and the energy you eat: if you maintain on 2,200 kcal and eat 1,800, your deficit is 400 kcal. Maintenance is what you burn on a usual day, and I wrote about finding it in how many calories should I eat a day.

You know neither number for sure, so I treat the deficit as a plan and the scale over a few weeks as the check.

How do I calculate my calorie deficit?

You calculate a calorie deficit in three steps:

Find your maintenance. Estimate your resting burn with the Mifflin–St Jeor equation and multiply it by an activity factor (1.2 if you mostly sit, 1.375 if you're lightly active). My calorie calculator does this.
Pick a pace. A kilo of body fat is about 7,700 kcal, so each pace has a daily deficit (table below).
Subtract. Maintenance minus the deficit is your daily target. If it lands below 1,200 kcal, stop at 1,200 and talk to your doctor.

Pace per week	In pounds	Less per day
0.25 kg	about 0.55 lb	275 kcal
0.5 kg	about 1.1 lb	550 kcal
0.75 kg	about 1.65 lb	825 kcal

Worked out as pace × 7,700 ÷ 7, the same as in my deficit calculator, which offers these three paces and never goes below 1,200 kcal a day. The NHS gives a simpler rule: cut around 600 calories a day, a little above the middle row.

Where does the 500-calorie rule come from?

The 500-calorie rule comes from the old idea that a pound of fat is 3,500 kcal (about 7,700 per kilo): 500 less a day is 3,500 a week, so a pound a week. It describes the first weeks well, but it overpromises over the long run.

Taken literally, 500 kcal a day for a year would take off about 52 lb (24 kg). Kevin Hall's team showed in The Lancet in 2011 why it doesn't work like that. In their model, every 100 kJ (about 24 kcal) a day less leads to an eventual weight change of about 1 kg, but half of it comes in about a year and 95 % in about three years. In their worked example, the static rule predicts about twice the first-year loss their model does.

For 500 kcal a day (about 2,090 kJ) that means about 21 kg in total, roughly half of it in the first year. Still a very good result, only slower than the rule promises.

Is a 1,000-calorie deficit too much?

A 1,000-calorie deficit doubles the speed on paper, but in practice it has two problems. Hunger is stronger, so the plan breaks sooner; that's what happened to me. And it easily takes you below 1,200 kcal a day, which you shouldn't do without talking to your doctor.

The CDC notes that people who lose weight at a gradual, steady pace are more likely to keep it off. I don't plan faster than 0.75 kg (about 1.7 lb) a week, and I'd rather stay at 0.25 to 0.5. If you're pregnant, breastfeeding, have a chronic condition or a history of eating problems, your doctor should set your deficit, not a calculator.

Why am I in a calorie deficit but not losing weight?

If you're in a calorie deficit but not losing weight, it's usually one of four things, in the order I check them:

Water. Your weight moves from day to day with salt, water and whatever is still in your stomach. I weigh two or three times a week in the morning and look at the two- to three-week average.
The deficit is smaller than you think. Oil, drinks and snacks are the things people forget to log. Check those before you cut portions.
Weekends. Five days at 500 below maintenance and two days at 1,000 above leave a deficit of only about 500 kcal for the whole week.
Your maintenance dropped. A lighter body burns less. Every 4 to 5 kg (roughly 10 lb) I recalculate and, if needed, lower my target by 100 to 150 kcal. The NIH Body Weight Planner does this for you.

How do I create a deficit without feeling hungry?

The easiest calorie deficit is one you don't feel, because calories hide in portions and extras more than in the dishes themselves. Swaps I've tried:

Instead of	kcal	Try	kcal	Saves
3 slices of white bread (40 g each)	320	1 slice	105	210
3 cans of beer, 12 fl oz (355 ml) each	460	1 can	155	305
2 handfuls of peanuts (60 g)	350	1 handful (30 g)	175	175
10 cevapi in a lepinja with kajmak	1,320	5 cevapi in half a lepinja with ajvar	640	680
a piece of meat burek with a glass of yogurt	845	half a piece with the yogurt	485	365

Source: my calorie tables, usual portions, rounded to 5 kcal; the savings come from the unrounded values, so they can be 5 off the difference of the rounded ones.

You don't need all five. Two slices of bread less at lunch and one can instead of three in the evening come to about 515 kcal, a full day's deficit without skipping a meal.

Notice what isn't in the table: "cut out bread" or "never eat burek again". Bans last me until the next family gathering; a smaller portion lasts.

How do I know I'm really in a deficit?

The scale tells you whether you're really in a calorie deficit, if you read the trend over weeks rather than one morning. If your average hasn't moved in three weeks, the deficit isn't what you think, so go back to the oil, the drinks and the snacks.

For me the hardest part was logging everything. So in Calorko, the Android app I'm building, you photograph your plate and get a calorie estimate with a range. A photo isn't a scale, but it beats a meal that never got logged.

In short

A deficit is the gap between what you burn and what you eat; 275 to 550 kcal a day is enough for most adults.
The 3,500-calories-per-pound rule fits the first weeks; later loss slows, so recalculate every 4 to 5 kg.
The easiest savings are in portions and extras: bread, drinks, snacks.
Don't go below 1,200 kcal a day without your doctor.