How to Calculate Your Calorie Deficit (Without Overcomplicating It)

If you're trying to lose weight, you've probably heard the term calorie deficit. It’s the foundation of fat loss — without a deficit, fat loss won’t happen. But how do you actually calculate it without overthinking or doing complex maths? In this guide, we’ll walk you through it step by step, using free calculators to make it simple.

Calculating Your TDEE (Total Daily Energy Expenditure)

The first step is to work out your TDEE — Total Daily Energy Expenditure. This is the total number of calories your body burns in a day, including everything from exercise to daily movement and even digestion. It’s essentially the number of calories you need to maintain your current weight.

The easiest way to calculate your TDEE is by using an online TDEE calculator. You’ll be asked to input your age, gender, height, weight and activity level. Make sure you select your actual activity level, not how active you think you should be.

Once entered, the calculator will estimate your TDEE. For example, if your TDEE is 2,500 calories, that’s roughly how many calories you’d need to eat each day to maintain your current weight.

Stay with me now, I know it's a touch hard to follow

Calculating Your BMR (Basal Metabolic Rate)

Your BMR — Basal Metabolic Rate — is the number of calories your body burns at rest. It’s the minimum amount of energy required to keep you alive and functioning.

Most TDEE calculators will also show you your BMR, but you can easily search for a BMR calculator online if you want to check it separately. You’ll need the same information: age, gender, height and weight.

Knowing your BMR is important because it helps you understand how many calories your body burns even without any activity. You should never eat below your BMR long-term, as it can negatively affect your health, energy, and metabolism.

Yes that's right you burn calories doing nothing!

Calculating Your Deficit

Once you know your TDEE, you can calculate your calorie deficit. This simply means eating fewer calories than your body burns, forcing it to use stored fat for energy.

The size of your deficit matters. A reduction of around 15 to 20 per cent below your TDEE is a good starting point. For example, if your TDEE is 2,500 calories, eating around 2,000 to 2,125 calories per day will allow for sustainable fat loss.

Many online calculators will allow you to input your fat loss goal and automatically calculate your deficit, so you don’t have to do the maths yourself.

A larger deficit might result in quicker fat loss but can leave you feeling drained, hungry and more likely to fall off track. It’s better to start moderate and adjust over time.

And trust that sticking to these figures will work, it's thermodynamics!

How to Stick to Your Deficit

Knowing your deficit is one thing — sticking to it is where the real work begins. It’s easy to underestimate how hard it can be to stay in a deficit consistently.

One of the best ways to stay on track is to track your calorie intake using an app like MyFitnessPal or Cronometer. Tracking helps you stay accountable and gives you a clear idea of what you’re actually eating.

What you eat also matters. Prioritising whole, nutrient-dense foods — such as lean proteins, fruits, vegetables, and whole grains — will help keep you fuller for longer. That said, there’s no need to cut out the foods you enjoy. Including treats in moderation makes the process far more sustainable.

Planning your meals and snacks ahead of time will also reduce the chances of overeating or blowing your calories out unexpectedly.

Lastly, remember that fat loss isn’t linear. Your weight will fluctuate day to day. What matters is your long-term consistency, not what the scales say after one or two days.

Good luck!