How to Calculate Your Calorie Deficit (TDEE Explained)

By Zerxus Team  |  Fat Loss

A calorie deficit is the difference between the energy you burn in a day, your total daily energy expenditure or TDEE, and the energy you eat. To calculate yours, estimate your TDEE, then subtract 15 to 25%. That target is your starting intake for fat loss. The important part comes next: you track your bodyweight for two to three weeks and adjust, because no formula predicts your exact numbers. The calculator gets you close; your own data makes it right.

Step 1: Estimate your TDEE

TDEE has four parts: your resting metabolic rate (the biggest chunk), the calories you burn digesting food, your training, and your everyday movement (NEAT). You can estimate the total with a quick calculation:

• Estimate your resting burn, then multiply by an activity factor: roughly 1.3 for mostly sedentary, 1.5 for moderately active, 1.7 or higher for very active jobs plus training.
• Or take the simple shortcut many coaches use as a starting point: around 30 to 33 calories per kg of bodyweight for a moderately active person.

Both are estimates. Treat the number as a hypothesis you are about to test, not a fact.

Step 2: Set your deficit

Subtract 15 to 25% from your TDEE. A smaller cut (around 15%) is easier to sustain and protects muscle; a larger cut (around 25%) is faster but hungrier. For most people, a deficit that produces 0.5 to 1% of bodyweight lost per week is the sweet spot. As a rough guide, a 500 calorie daily deficit tends to yield somewhere near 0.5 kg of fat loss per week, though individual results vary.

Step 3: Track and adjust

This is where fat loss is actually won.

1. Weigh yourself most mornings and take a weekly average. Daily weight is noisy; the weekly trend is the signal.
2. After two to three weeks, check the trend. Losing at your target rate? Hold. Not losing? Trim intake by 100 to 200 calories or add steps.
3. Repeat. As you get lighter and adaptation kicks in, you will need to adjust again. Our guide to metabolic adaptation explains why.

Don’t forget protein and training

A deficit decides how much weight you lose. Protein and lifting decide whether it is fat or muscle. Keep protein around 1.6 to 2.2 g per kg (see our protein guide) and keep training hard so your body has a reason to hold onto muscle. Losing weight without resistance training means losing some hard-won muscle along with the fat, which is covered in our guide to losing fat without losing muscle.

A worked example

Say you weigh 80 kg and are moderately active. A quick estimate puts your TDEE somewhere around 2,600 calories. A 20% deficit lands you near 2,080, so you round to a practical 2,100 and eat there for a fortnight. Your weekly average weight drops by about 0.5 kg, which is roughly on target for your size, so you hold. Three weeks later the loss slows to almost nothing, a normal sign of a lighter body and some adaptation, so you trim to 1,950 or add 2,000 daily steps and the trend resumes. Notice that you changed one variable at a time and let two to three weeks of data guide each move. That patience is what separates steady progress from the crash-and-stall cycle.

The same method scales to any starting point. The numbers will differ, but the loop does not: set a target, hold it long enough to read the trend, then make the smallest change that gets things moving again.

Frequently asked questions

How big should my calorie deficit be?

For most people, 15 to 25% below maintenance works well, producing around 0.5 to 1% of bodyweight lost per week. Smaller deficits are more sustainable and better protect muscle; larger deficits lose weight faster but bring more hunger and fatigue. Very aggressive deficits rarely last and tend to cost muscle, so err toward moderate unless you have a specific short-term reason to push harder.

Are online calorie calculators accurate?

They give a reasonable starting estimate, but they cannot account for your exact metabolism, daily movement, or how much you underestimate portions. Use a calculator to set an initial target, then trust your bodyweight trend over two to three weeks to tell you the truth. If you are not losing at the expected rate, your real TDEE differs from the estimate, so adjust your intake to match.

Why am I in a deficit but not losing weight?

The most common reason is that the deficit is smaller than you think, usually from untracked bites, generous portion estimates, or an overestimated TDEE. Water retention can also mask fat loss for a week or two. Tighten your food tracking, weigh portions, and judge progress on a two to three week weekly average rather than the daily scale.

The bottom line

Calculating a calorie deficit is estimate, then verify. Guess your TDEE, subtract 15 to 25%, then let your weekly weight trend correct the guess. Keep protein high and keep lifting, and the weight you lose will be the weight you want to lose. Zerxus tracks your training alongside your progress so you can adjust with confidence. Start your plan at Zerxus.

Zerxus Coaching Team

Certified Strength & Conditioning Coaches

The Zerxus coaching team combines qualified personal trainers, certified strength coaches, and evidence-based sports science to build programmes that actually work. Every article is grounded in peer-reviewed research and practical coaching experience — no fads, no shortcuts.