How to calculate energy needs at target weight?

In general, to determine your dialy energy needs, you need to take into account the following:

  • your weight
  • your age and sex
  • your average level of activity

In adherence to Asymptotic Nutrition Approach, we will not seek to calculate your current energy needs, but your energy needs at your target weight. So the first step is to determine your target weight. Once this is done, we procede to calculating your energy needs at that target weight. And then, according to theory behind Asymptotic Nutrition Approach (which is in fact, just simple maths) – if you consume that amount of calories, your actual weight will over time asymptotically approach your target weight.

To calculate daily energy needs, dieticians use various formulas and calculators. As you’ll see later in the article, calculating daily energy needs can be quite tricky, as different formulas and different calculators give very different estimates. Luckily there is a way to overcome this, as you’ll see.

Also, if you visit a dietician, they can more precisely estimate your daily energy needs at your target weight, using more advanced methods.

Here are some calculators that can help us determine daily energy needs:

The first one comes from Australian Dietary Guidelines:

You insert your gender, age, weight and activity level. It’s assumed that you insert your current weight, but for our purposes, you insert your target weight.

So in my particular case, it goes like this:

MALE, 33, Weight = 79 kg (this is target weight, at BMI 25), activity level 1.4 (sedentary work and no strenuous leisure activity)

And the calculator gives me energy needs of 10,423kJ, for the convenience purposes we convert it into calories (1 kilojoule = 0.239 kilocalories – note: “calories’ mentioned in nutrition talk are acctually kilocalories – kcal) and it gives me that my daily needs are 2491.15 kcal.

This means, that with my usual sedentary lifestyle, if I want to reach my target weight of 79 kilos, I should be cosuming on average 2491.15 calories per day. If the calculation is correct, with long term consumption of this amount of calories, and with no changes in my physical activity – I will be asymptotically approaching this weight, and in around 1-2 years, I will be very close to my target weight. Very important thing to note is that I need to permanently switch to this caloric intake for it to work. Even if I am very near my target weight, I should keep consuming this amount of calories.

But let’s find out two other things:

first, let’s find out why my current weight is 86 kg? The answer is, because my average daily caloric intake is such to lead me to an equilibrium at that weight.

So, now, in the calculator, I will insert the following:

MALE, 33, Weight = 86 kg, activity level 1.4 (sedentary work and no strenuous leisure activity):

and the calculator gives me daily energy needs of 10,893kJ, which is 2603.5 calories.

Since my weight is stable right now, this means that this is in fact the amount of calories I am consuming daily on average.

So the underlying reason behind my current weight is that my average energy intake is around 2603.5 calories per day.

So, in the long term, to reach my target weight, all I should do is lower my daily energy intake from 2603.5 to 2491.15 calories per day. The difference is only 112.35 calories. It is just 4,31% of my standard calorie intake. It’s the energy you find in 50 grams of bread… 2 small slices. So just by subtracting, say two small slices of bread from my usual food intake would be sufficient to achieve this goal.

But, let’s see what happens if I add a bit more physical activity to the calculation. My next input is:

MALE, 33, Weight = 79 kg (target weight), activity level 1.6 (mostly sedentary work with little or no strenuous leisure activity – students, lab assistents, drivers):

11,912kJ = 2847.03 calories

Now that’s a big difference! This says that if I adopt this activity level, I will reach my target weight of 79 kilos, even if I increase my daily food intake slightly. So if I become more physically active, even with 243,53 extra calories (2847.03 – 2603,5), I will still lose weight until I arrive at 79 kilos.

But here we need to be cautious and pay a lot of attention!

Increasing your activity level from

1.4 (sedentary work and no strenuous leisure activity) to 1.6 (mostly sedentary work with little or no strenuous leisure activity – students, lab assistents, drivers) seems like nothing, but it is actually a big deal, and it’s very hard to accomplish without changing your job.

We’re mostly defined by what we do at work during these 8 hours or so. If you keep your same office job, you’d need to make relatively big changes in the rest of your day to really achieve this change in activity levels.

Let’s just take a closer look. At 79 kilos, with activity level of 1.4 – I would need 2491.15 calories per day, while at activity level 1.6 – I would need 2847.03 calories. This is 355,88 calories difference.

This is calories burned in around 72 minutes of walking, or 29 minutes of moderate cycling. And you’d need to do it every single day (if you wish to remain reach 79 kilos with this food intake of 2847,03 calories).

So let’s go back to where we started.

My actual weight = 86 kilos and with my sedentary lifestyle I usually consume 2603,5 calories, at which point my weight is at equilibrium.

To reach my target weight of 79 kilos, with the same level of activity, I need to consume 2491.15 calories per day, that is, to lower my energy intake by 112.35 calories.

However, as I am certainly not a seriously overweight person and this small calorie intake change is very easy to make, I could also, alternatively stay at the same level of average energy intake – 2603.5 calories and find a way to just add 112.35 extra calorie expediture in my daily life.

I start with the same starting point:

at 79 kilos, with sedentary lifestyle, I need just 2491.15 calories per day. But if for some reason I don’t want to lower my food intake, I need to spend 112.35 extra calories each day, so that I am at equilibrium at 79 kilos (instead of 86) at my current food intake level of 2603.5 calories.

To burn these 112.35 extra calories I would need to add around 22.5 minutes of walking every day. Just by adding 22.5 minutes of extra walking (if I already used to walk, I don’t count previous levels of walking, just extra, additional walking), over 1-2 years, with the same level of food intake, I would go from 86 kilos to 79 kilos.

It could be done every day, or it can be distributed in longer walks of 52 minutes, 3 times a week for example. It doesn’t sound like a big deal, bit it’s not a small addition to activity levels.

Now, let’s try another calculator. As you can see we’ll have a huge problem with calculators, as they tend to give us wildly different estimates of daily energy needs. But luckily there’s a way to overcome it.

But before we try a new calculator, let’s summarize what we learned about my case so far.

Current weight86 kg (BMI = 27,23)
Estimated current calorie intake2603,5 calories per day (assuming sedentary lifestyle)
Target weight79 kg (BMI = 25)
Energy needs at target weight2491.15 calories (assuming sedentary lifestyle)
Difference between current calorie intake and calorie needs at target level112,35 calories
Ways to reach target weightEither consuming 112.35 calories less than usual (with no changes in activity level) or spending 112.35 extra calories on physical activity (say – three 52 minutes walks per week)
Note: Perhaps, the best strategy would be to combine eating less and adding exercise, for example, to achieve the same calorie difference, one could consume 61 calories less, and add 61 calories of activity per day (for example three 26 minute walks per week).

Now to the next calculator:

Total Daily Energy Expediture is another popular daily calorie needs calculator. However, it gives me completely different results, for the same input. It usually gives much lower calorie needs figures. BTW, this one also takes into account height. Let’s input my data:

MALE, age: 33, height: 178 cm, weight (target weight) = 79 kilos, activity level – sedentary – optionally I could also enter body fat percentage.

It gives that my daily needs at target weight of 79 kilos are 2091 calories per day. (It’s whole 400 calories less, than the estimate by Australian Dietary Guidelines !!! )

But let’s see, what are my energy needs at my current weight of 86 kilos, which is good to know, because, since my weight is in equilibrium right now, that’s how many calories I actually consume per day, according to them. So my next input is:

MALE, age: 33, height: 178 cm, weight (current weight) = 86 kilos, activity level – sedentary.

And what they say is that my current energy needs are 2175 calories per day. (428 calories less than the estimate by Australian Dietary Guidelines )

According to Total Daily Energy Expediture calculator the difference between my current intake level (2175 calories) and the level I would need at my target weight (2091 calories) is 84 calories.

And this is really the most important piece of information: this difference between two intake levels – that is how many calories less I need to consume, or how many more calories I need to spend, in order to reach target weight.

Luckily, despite wild differences in estimates of daily energy needs by various formulas and calculators, when it comes to calculating the difference between intake levels for different weights, calculators give much closer results: for example Australian Dietary Guidelines gave me that I need to make correction for 112.35 calories, while TDEE gives me that the difference is 84 calories. This level of variance is much more acceptable.

Now there are a couple of take home messages:

  • different calculators give very different estimates of your daily energy needs at a given weight level, therefore it’s quite tricky estimating your true daily energy needs at certain weight
  • this makes it very hard to create a nutrition plan from scratch aiming at certain daily calorie intake and to be sure that it will work in sense of helping you approach certain weight if you follow it.
  • However, different calculators give much closer estimates of difference between energy needs at different weights.
  • You must use the same calculator for estimating calorie needs at both weights, because calculators aren’t compatible between themselvs. Choose one and stick to it. What you really want to find out is how much calorie difference you need to make from your current energy intake.

For the end of this article I’ll give you another table where we compare it all between Australian Dietary Guidelines and TDEE:

Australian Dietary GuidelinesTotal Daily Energy Expediture
Current weight86 kg (BMI = 27,23)86 kg (BMI = 27,23)
Estimated current calorie intake2603,5 calories per day (assuming sedentary lifestyle)2175 calories per day (assuming sedentary lifestyle)
Target weight79 kg (BMI = 25)79 kg (BMI = 25)
Energy needs at target weight2491.15 calories (assuming sedentary lifestyle)2091 calories (assuming sedentary lifestyle)
Difference between current calorie intake and calorie needs at target level112,35 calories84 calories
Ways to reach target weightEither consuming 112.35 calories less than usual (with no changes in activity level) or spending 112.35 extra calories on physical activity (say – three 52 minutes walks per week)Either consuming 84 calories less than usual (with no changes in activity level) or spending 84 extra calories on physical activity (say – three 40 minutes walks per week)
Note: Perhaps, the best strategy would be to combine eating less and adding exercise, for example, to achieve the same calorie difference, one could consume 61 calories less, and add 61 calories of activity per day (for example three 26 minute walks per week). Perhaps, the best strategy would be to combine eating less and adding exercise, for example, to achieve the same calorie difference, one could consume 42 calories less, and add 42 calories of activity per day (for example three 20 minute walks per week).