How Many Calories Should I Eat a Day to Lose Weight?

By Lindsay Wilson

How many calories should I eat a day to lose weight? As many as you can while losing at a healthy rate (0.5-1% of bodyweight per week).

When the Nobel prize winning physicist Isidor Isaac Rabi died in 1998 a lovely story came to light. It goes a little something like this.

A good friend once asked him:

Why did you become a scientist, rather than a doctor or lawyer or businessman, like the other immigrant kids in your neighborhood?

His response was delightful:

‘My mother made me a scientist without ever intending it. Every other Jewish mother in Brooklyn would ask her child after school: ‘So? Did you learn anything today?’ But not my mother. She always asked me a different question. ‘Izzy,’ she would say, ‘did you ask a good question today?’ That difference – asking good questions -made me become a scientist’

‘How many calories should I eat a day to lose weight?’ is a very good question. What you put in your mouth determines whether or not you’re in a deficit, and is the primary factor in whether or not you are losing weight. For super active people weight loss might be possible at 4,000 calories a day, while some people may have to go down to down as low as 1,200 to shift fat at an adequate rate.

In this third section of The Fat Loss Framework we going to look at different ways to set calories for fat loss. We’ll look at fixed targets, online calculators, bodyweight multipliers, tracking maintenance and target rates of weight loss.

Fixed Calorie Targets for Men and Women

Using a fixed calorie target for women and men is commonplace. Fixed targets are simple to communicate, make it easy to build generic meal plans and will work on some level for a majority of people (because the guidelines are sufficiently low to work for the majority of the population).

But here’s the thing.

You aren’t average and your needs will change over time. A one size fits all approach will often result in you getting an inappropriate caloric intake, and promote inflexibility when weight loss stalls. You can do much better.

If your aren’t sure of what I mean by a fixed target, let me give you an example. The National Health Service in the UK dispenses the following advice to help people achieve healthy weight loss of 0.5kg to 1kg (1lb to 2lb) each week.

For most men, this means sticking to a calorie limit of no more than 1,900kcal a day, and 1,400kcal for most women.

Now for the ‘average’ man or woman this is great advice, but only because it is designed for the average. Let me show you what I mean.

These figures have their origin in data suggesting that the typical British female needs 2,000 calories a day to maintain a healthy weight, while for a male the figure is 2,500. From this they simply subtract 600 kcal a day, which is the size of NICE’s deficit guideline for sustainable fat loss. Here it is visually.

Now as far as a ‘one size fits all’ approach goes this is pretty good, and from a public health perspective you can understand the appeal of simple targets. But you’d never use this with a client.

A 25 year old women who spends her working day on her feet and plays a sport could be easily expend 3,000 kcal/day. Putting her on an intake 1,400 kcal a day would just be cruel. Sure she lose weight, but she might also lose muscle mass, concentration, immunity, metabolic rate, her menstrual cycle . . . Yet 1,400 might be the ideal amount for a desk bound 60 year old who only expends 1,800 calories a day.

Bottom line: Fixed calorie targets are too simplistic to be useful

Use an Online Calorie Calculator

The most common solution to the problem of overly simplistic fixed targets is to use an online calculator. Online calculators are a much better way to go than fixed estimates, but you need to realise they are only an estimate. Moreover, they are only as good as the information your feed them, which is actually quite hard to get right.

The standard approach I see across the fitness space is to calculate resting metabolic rate first, then multiply by an activity factor to get the total daily energy expenditure, then take away a fixed amount (~500 kcal), or a percentage (~20%), to set a target with a decent deficit.

Now on face value this seems like an excellent idea, but once again its treating you like the average. And in one way it is almost worse. In my experience the process of imputing individual details like gender, height, weight, age and activity level naturally leads people to think online calculators are highly accurate, when they are anything but.

When people then eat based on these recommendations and the results are lacklustre they often lose faith. This is particularly sad when they are doing a really good job of hitting the target they were set, but the calculation is simply miles off.

Now obviously I’m a data person, so I don’t expect you to believe my assertion that online calculators are inaccurate without some proof. So let’s unpack a calculation.

The best available equations for resting metabolism are the Mifflin-St Jeor:

Men: REE = 10 x weight (kg) + 6.25 x height (cm) – 5 x age (years) + 5
Women: REE = 10 x weight (kg) + 6.25 x height (cm) – 5 x age (years) – 161

If you read the original paper that proposed these equations they state quite clearly that:

there is a variability of 30% in REE that cannot be explained on the basis of the variables assessed in this study. This may be due to individual differences in genetically determined or acquired metabolic efficiency, which merit further investigation

So although these are the best equations we’ve got, they still only explains 70% of the variation in resting metabolic rates. We know from a later study that 70% of estimates for the obese using this equation were accurate within ±10%, while the total range was ±20% or so.

To help you understand this a little more here is what resting energy expenditure looks like when graphed against weight (which itself explains 57% of variation). The data I’ve used is measurements for 645 adults aged 20-70 years old from the Database of Doubly Labelled Water from the Institute of Medicine in the US.

The orange lines are the best fit for men and women. You can see that because men tend to have more muscle and larger organs their resting metabolic rates tend to be about 300 calories higher than women at any given bodyweight.

Now to be honest I haven’t got much of a problem with how on-line calculators work out resting metabolic rate. Sure it isn’t perfect, but it is close enough to be useful, and much better than using fixed numbers. What happens next is the real issue.

You take an estimate which already has a degree of variablity (±20%), and then multiply it by an activity multiplier which is very hard to estimate well.

Here are the most typical multipliers you see:

Sedentary = 1.2 (little or no exercise, desk job)
Lightly active = 1.375 (light exercise/sports 1-3 days/week)
Moderately active = 1.55 (moderate exercise/sports 6-7 days)
Very active = 1.725 (hard exercise every day, or 2 xs/day)
Extra active = 1.9 (hard exercise 2 or more times per day)

Now I understand this makes putting a calorie calculator together possible, but getting these multipliers right is very hard. Also pretending they are largely determined by how much you exercise is plain false. They are a complex function of genetics, work life, exercise patterns, muscle mass, postural control, propensity to fidget . . .

Let’s check the data again to show you what I mean. Here’s what physical activity level looks like when graphed against age.

The average physical activity level (PAL) in this dataset is 1.7, so is the median. Over 80% of people fall somewhere between 1.4 and 2.1. The small orange ‘line of best fit’ gives you an idea of the average, but this barely explains 6% of variation.

The things likely to take a person above 2 are a physically active job, endurance training or being one of those lucky fidgety folk that are wired to burn excess food. Going below 1.5 is likely to involve a desk job and much more common in older people.

My point in analysing this data is not to trash online calculators. I just want you to view their results with the scepticism they deserve. Not only are they potentially inaccurate but they tend to promote the problematic idea that calorie targets should be static. This is not the case.

Fat loss is state specific. A good caloric intake is the one that produces a healthy rate of fat loss without stressing your body too much. This figure is different for all of us and will change over time depending on what phase of a diet you we are in, and how much fat we are carrying.

If you are still interested in using an online calculator I recommend the BodyWeight Planner developed by Kevin Hall’s group at the National Institute of Health. Although it is based on similar calculations its treatment of activity levels is more sensible. Moreover the whole calculator is built on a dynamic model of metabolism which makes it many fold more realistic than most. Just remember the starting expenditure might not be completely accurate.

Bottom line: Online calculators are rough estimates at best

Multiply by Bodyweight?

For people who aren’t prepared to track their food intake my preferred method for setting calories is simply to multiply bodyweight by an activity multiplier that reflects their lifestyle. This can give you a decent starting range which you can then adjust based on results.

Based on data, as well as experience, I find most people can lose at a decent rate beginning around 12 kcal/lbs. If you’ve got a job where you are on your feet all day, or exercise a lot, you’d certainly want to start higher than this. Perhaps at 14 or 16 kcal/lbs, or even higher if you are quite light and move a lot.

The more you can eat while losing fat the better really. Someone who can start losing at 14 kcal/lbs is going to have a far nicer journey than someone who jumps straight down to 10 kcal/lbs. At the same time you also need to get results early on, because results are motivating. There is evidence that people shift more weight early on often do better in the long run. Given this people carrying a lot of fat should probably be more aggressive, as their body can take it, whereas leaner individuals need to be more careful of their metabolic rate.

I can’t just recommend a single multiplier (like 12 kcals/lbs) for two reasons. Firstly weight only explains 35% of the variation in total energy use, so using weight alone it isn’t ideal. Secondly we know that the body will adapt to energy restriction. So someone who starts their cut at 14 kcals/lbs can easily end up grinding out days at 10 kcals/lbs to keep things going as they lean out. Higher is always preferable because it implies a faster metabolic rate, but only as long as its working.

Let’s see how these multipliers look against some real data point for total energy expenditure.

The dots on this chart are the total energy expenditures for 645 adults aged 20-70, graphed against their weight. To lose fat they would each need to create deficit by eating less that where they are. Some examples are shown with the grey arrows.

A sensible deficit to get things moving might be somewhere from 400-1,000 kcals below maintenance, or about 20% off our total. Using the ‘typical’ figure of 12 kcal/lbs will do a good job of this for the third of people with average energy use. For active people (towards the top of the graph) this will be too low. For the less active third (at the bottom) it might be too high to work well. And for an unlucky 8% of people on this chart 12 kcal/lbs will actually put them in a surplus, so they’ll need to dig deeper or add activity.

To show you just how varied energy needs can be lets graph energy use in terms of calories per pound of bodyweight (kcal/lbs).

This graph shows you why individual context is essential for setting calorie intake!

The top of this graph is a twenty six year old woman that requires 3,500 calories to maintain her 120 lbs bodyweight. Contrast this to the lowest figure which is a 55 year old woman that needs just 2,000 calories to maintain 245 lbs bodyweight. Nine out out of the ten lowest numbers are woman above the age of 50, who each require just 9 kcal/lbs to maintain weight at their current activity level.

The two orange lines of best fit give us some insight that heavier people will likely need to eat fewer calories per pound to lose weight. We can see why the classic body-builder range for cutting of 10-12 kcal/lbs makes a lot of sense for heavier men. In contrast lighter people should avoid jumping straight in at low multipliers as this may leave them eating too few calories.

Active young women with low bodyweight (<120 lbs) should be particularly careful above using multipliers under 12 kcal/lbs as this is likely to take them below the basal metabolic rate and if combined with strenuous exercise can trigger amenorrhoea (the loss of menstrual cycle). This is disturbingly common among young women who compete in endurance, aesthetic and weight class sports.

Lastly it is important to stress again that energy expenditure declines in response to dieting. So you may need to adjust you calories downward to keep things moving. A typical body-builder could easily visit 14, 13, 12, 11 and 10 kcal/lbs during a prep, despite falling bodyweight.

So don’t be disheartened if you too need to adjust as time goes by, and remember that adjusting shouldn’t always mean less. Increasing calories has its time and place, whether it be in terms of refeeds, calorie cycling, as a diet break or moving back to a healthy maintenance following weight loss.

Bottom line: Bodyweight multipliers are simple and flexible

Track Maintenance Calories First

The world’s leading experts at losing fat are natural body-builders. And in the weeks before they start their 15-30 week competition prep they track the calories (via macros) in everything they eat, as well as weighing their body each morning.

If they find themselves eating 2,800 calories a day, and stable at their current weight, then that is their ‘maintenance calories’. From here they can simply subtract a sensible amount, say 500 kcal, and get to work eating an average of 2,300 each day until things start to slow, when they might add in some cardio.

Tracking your diet for a week or two before you start trying to lose fat takes the guess work out of the calorie setting process. Yes it is a tedious thing to do and you need to do it properly, with a digital food scale and an app (like MyFitnessPal), but there is simply nothing more effective.

If you have any aspiration to one day reach very low levels of body fat then taking a couple of weeks to track maintenance first is a superb investment of your time. It will likely save you considerable time, doubt and energy further down the line. For people with physique based goals it is simply an investment worth making.

The clever thing about tracking first is that even if you aren’t perfect (no one is), you will still nail your deficit. This is because any miss-measurement you do while tracking maintenance is likely to be carried through to your fat loss diet. So even if your baseline is a bit sloppy, your deficit should be pretty tight.

Tracking is certainly not something for everyone, but it is tremendously educational. Even if you only do it for a couple of weeks you will learn a lot about the energy content of different foods. A super valuable skill for people losing weight.

As a rough guide to logical ranges for maintenance calories I’ve cut two graphs.

Let’s start with women.

The first thing to stress here is there is simply huge variation. The range is from below 1,300 kcal/day to above 3,600 kcal/day. The average is around 2,400.

Although we can see that energy requirements typically increase as women get heavier (the orange line), this only accounts for about 20% of the variation. Activity levels are actually a much more important explainer of energy needs, accounting for close to 40% of the variation.

So if you have a busy job that keeps you on your feet, or you do a lot of sport, you’ll may come in above this orange line. If you have a desk job, and are pretty sedentary outside of work, you’ll likely be much lower. Genetics is part of this too. Some people towards the top left of this graph are probably far better programmed for burning excess food, whereas those towards the bottom right will be more likely to store excess food.

Let’s have a look at something similar for men.

Once gain we see great variation, ranging from below 1,800 kcal/day to over 4,800 kcal/day. The average is higher for men, at around 3,100 kcal/day.

Weight explains around 30% of the variation in energy use among men. Activity levels do better, accounting for almost half of what is going on. This means that if you spend your entire day stuck at a desk you are likely to be well below the orange line, even if you lift ;-).

If you really want to know your own maintenance is then the best bet is to track it. Apps like MyFitnessPal have made this process considerably easier in recent years, and for people who have tried a lot of other approaches and struggled a little bit of tracking can be extremely eye opening.

Lastly, don’t forget that these numbers are for people at stable weights. If you have recently lost weight then your body will be running pretty efficiently in an attempt to defend fat mass. This means your current maintenance could easily be below ‘average’ for your weight.

Bottom line: Tracking is the most accurate way to set calories

Adjust Calories Based on Results

At the top of this page I wrote about the virtue of asking a good question. For about 3,000 words now I’ve had a decent crack at answering the following:

How many calories should you eat a day to lose weight?

I think this is a very good question. Because it focuses the mind on the need to create a caloric deficit, which is of primary importance when losing fat. Of course just because I think this is a good question doesn’t mean we can’t improve upon it. And there is a subtle way we can shift this question to make it a great one.

Here it is:

Is , calories a day working for me lately?

You see this question forces you to reveal if you’ve found a consistent way of controlling your calories and measuring your results. This is actually quite revealing. If someone can tell you their average weekly weight loss and mean daily calories you can be pretty sure they have the skills needed to lose weight in style. Let me give you an example.

Let’s say your a 35 year old mum, with two young kids, working a desk job three days a week and have limited time for exercise. You weighs 170 lbs (77kg) and want to lose 20lbs. You don’t want to ‘waste 2 weeks’ tracking your maintenance, but are happy to try YouTube workouts 3 nights a week.

Based on your weight, age and activity levels you’re guessing your maintenance falls around 2,300 kcals/day. If your were super patient you’d start a 2,000 calorie meal plan (with adequate protein, fats and carbs). But you need to see some results, so you jump in at at 1,700 instead.

After four weeks of pretty solid adherence the results are in. Here are some possibilities.

You’ve lost 9 pounds. Despite feeling crap, and hungry all the time, you’re delighted
You’ve lost 5 pounds. You’re crushing the workouts, like the food, but a little frustrated
You’ve lost 2 pounds. You’re fine and getting stronger, but very frustrated about the scale

Now here’s the funny thing. In every one of these cases you have succeeded is answering whether 1,700 calories a day is working for you over the last four weeks. This is a period long enough to separate the real weight loss trend from water weight fluctuations. And based on this information you can make really good adjustments.

In the first case it turns your maintenance might have been as high as 3,000 a day, in the second it could be closer to 2,400 and in the third case 2,000 or lower. Of course you can’t be sure exactly, because measuring food isn’t that accurate and fluctuations in water weight can distort scale weight. But nonetheless you are now superbly placed to make adjustments. Over the next month you could aim to lose a further 4 pounds. In the first case you’d bump up to 2,000, in the second hold tight at 1,700 and in the third case dig down 1,400.

In each case you have succeeded, because you’ve been patient enough to answer the question ‘how is 1,700 calories is working for me over the last 4 weeks’. Whether or not you were actually hitting 1,700 isn’t the point. As long as you’ve been consistent that doesn’t matter, you’ve got rough baseline to work from.

When it comes to precise numbers it is always hard to tell how accurate people are with their food. You see being accurate is actually very difficult. Many studies show how bad we are at counting calories (or macros). Even when trained dietitians where tested they we found to under-report by 220 kcal a day.

In fact the only population of people obsessive enough to have numbers worth trusting, in my view, are natural body-builders. Why? Because the chances are whatever they ate went on a digital food scale first. If they add oil, or sugar, or ketchup, they count that too. They aren’t messing about.

To give you a realistic idea of just how low body builders end up taking their calories during a contest prep I’ve put together a chart from a 3DMJ video comparing their macros during the lowest days of their prep. Just to be clear, these are the lowest days of the prep, most of it would have been far less aggressive.

Once again, the variation is incredible. Kevin Riley got shredded to the bone without going below 3,200 calories a day, while Nicole Hastings had to cycle down as low as 1,000 on some days.

Despite the fact that all these athletes all lift heavy, track their macros meticulously and have adjustments made by just a few coaches (with similar philosophies) there is huge variation between them. Alberto Nunez gets ripped without going below 18 kcal/lbs, where as Chris Lavado (Yucky) has to plumb the depths of 8 kcal/lbs.

How can the range across these athletes be so extreme? Well we’ve already seen that energy needs vary hugely between people. But on top of this the metabolic adaptation to energy restriction varies greatly between people too. So those with thrifty metabolisms can end up going very low to get lean.

Now just to be clear. The dedication that natural body-builders have to nutrition is pretty much unparalleled in sport. It’s probably not something for you, and its certainly not something for me. But we don’t need to act like a body-builder to learn from what they do.

Here’s the cliff notes:

They control their energy intake (via counting macros)
They assess what this does to their body (morning weigh ins)
They adjust based on results (weight, strength, mood, sleep)

That’s all it is. Do something consistent, see how that works out, adapt as required. Body-builders may be more accurate, patient and committed than normal dieters, but the physiology is all the same.

Bottom line: Adjusting calorie intake based on results is best practice

A Target Rate for Weekly Weight Loss

When it comes to calories, the proof is in your pudding. If you are losing at an average of 0.5-1% of your bodyweight each week, while maintaining strength, then you are nailing your calories!

I don’t care if you’re flexible dieting, eating paleo, intermittent fasting, clean eating, weight watching or low carb. If you’ve found your way into that zone, and you aren’t giving up strength, your weekly calorie intake is probably very good. So whatever you are doing you want to ride that out phase out till the wheels fall off.

The 0.5-1% is a common recommendation based on evidence suggesting moderate rates are more muscle sparing. While slower than 0.5% can be great on a physiological level, it is often too slow to keep people motivated and results in very long diets. Losing faster that 1% is opposite. It is great for motivation, but when sustained for any length of time it’s generally a sign you’re burning up muscle mass or putting a lot of pressure on your hormonal health. This can reduce your metabolic potential in long run making results harder to maintain.

Percentages are used rather than absolute values, like 1-2 lbs a week, because it prepares lighter people for the reality that their progress will be slower.

Here’s what it looks like across different bodyweight ranges:

These numbers are pretty self explanatory. But how fast you aim should probably depend on how lean your are. If you’ve got a lot of fat to lose you want to be up at 1% to begin with whereas trying to get really lean requires a more patient approach. Let’s compare some rates.

Rapid (1.5%): Risks muscle loss. Only for a flying start (water weight)
Fast (1.0%): Ideal target for people with moderate/high body fat
Steady (0.5%): Smart target for lean men and smaller women
Recomp (0.0%): Occasionally useful for people new to weight training

Just to be clear there are no absolute rules here, they are just a guide. We are essentially trying the to balance the importance of early results against the risks extreme methods pose in terms keeping weight off.

For people who are carrying a significant amount of fat I really like 1% per week. If you can get the process started at 1% a week and then watch this dwindle to 0.5% as the weeks go by you are probably striking a very nice balance between motivating results and sustainable methods.

Bottom line: 0.5-1% of bodyweight is a sensible guide