How to Calculate a Calorie Deficit in 4 Steps

Knowing how to calculate a calorie deficit is what separates people who actually lose weight from people who slash carbs in a panic and stall within three weeks. The math fits in four lines, takes about 10 minutes to finish, and works for anyone who isn't dealing with a special clinical condition.

The problem is rarely doing the math. It's getting the size right. A deficit that's too small never moves the scale. One that's too big tanks your metabolism and brings the weight back in a yo-yo. There's a safe range, and it sits in a surprisingly narrow window. A sensible calorie deficit to lose weight lands between 300 and 500 kcal below maintenance for most people.

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Your deficit number, meal by meal, without typing a thing

In ContaCal, the AI cross-checks your daily target against every photo of your plate and shows the balance instantly.

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What makes a deficit "functional"

A functional calorie deficit meets three conditions. It sustains fat loss of roughly 0.5 to 1.5 lb (0.4 to 0.7 kg) per week, preserves lean mass, and fits your routine without wrecking your energy or mood. Anyone outside that range isn't in an "accelerated deficit." They're in starvation mode, which is a different thing entirely.

The reference model comes from meta-analyses in the American Journal of Clinical Nutrition, which show consistent results with cuts of 300 to 500 kcal per day below maintenance. For the conceptual deep dive, see the guide on the calorie deficit.

Step 1: find your TDEE precisely

Total Daily Energy Expenditure (TDEE) is the foundation of the calculation. Without it, the deficit is a guess. TDEE adds up your basal metabolic rate (60% to 75% of the total), the thermic effect of food (10%), planned exercise (10% to 20%), and the spontaneous movement you do all day.

The most widely used formula is Mifflin-St Jeor, validated in comparative studies as the most accurate for most adults:

• Men: (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5
• Women: (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161

That result is your basal metabolic rate. To reach TDEE, multiply by your activity factor: 1.2 sedentary, 1.375 lightly active, 1.55 moderately active, 1.725 very active, 1.9 athlete.

If you want help turning that number into a daily target, the guide on how many calories you should eat per day walks through it.

Step 2: set the size of the cut

There are three cut ranges, and each one fits a different profile. Picking the wrong one here is the single most common reason a diet stalls before the second month.

The aggressive cut without supervision is the biggest source of yo-yo dieting. People grind through four weeks, quit in the fifth, and regain the weight in three months. The moderate range loses less per week but holds the result longer, which is what actually matters.

Step 3: subtract the cut from your TDEE

This is the line that defines your daily calorie target. Take your TDEE, choose your cut, and subtract. The final number is the ceiling of what you can eat in a day and still be in a deficit.

A practical example with a 32-year-old woman, 154 lb (70 kg), 5'6" (168 cm), lightly active. Mifflin basal rate: 10 × 70 + 6.25 × 168 − 5 × 32 − 161 = 700 + 1,050 − 160 − 161 = 1,429 kcal. TDEE with the 1.375 factor: 1,429 × 1.375 ≈ 1,965 kcal.

Applying a moderate 400 kcal cut, her daily target lands at 1,565 kcal. That's the number she logs in an app, a notebook, or her head, and measures every meal against.

The target comes from the math, the balance comes from the camera. Two automated steps

ContaCal sets your number and closes the day's balance on a single screen.

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Step 4: split the target across meals

A daily target in your head is different from a daily target you actually execute. Splitting it by meal keeps you from reaching the evening with barely any budget left and having to skip dinner. For a 1,565 kcal target, a functional split looks like this:

• Breakfast: 350 to 400 kcal (22% to 25% of the total).
• Morning snack: 150 to 200 kcal.
• Lunch: 450 to 500 kcal (28% to 32%).
• Afternoon snack: 150 to 200 kcal.
• Dinner: 400 to 450 kcal (25% to 28%).

People who train in the afternoon usually swap the afternoon snack for a pre- and post-workout meal totaling 250 to 300 kcal. Detailed per-meal logging is what keeps the split honest across the week.

The safe range by profile

There's a calorie floor that protects your health, and it isn't the same for everyone. The limits below reflect guidance from the Institute of Medicine and the Academy of Nutrition and Dietetics.

• Adult women: never below 1,200 kcal without medical supervision.
• Adult men: never below 1,500 kcal without medical supervision.
• Athletes and active people: respect the equivalent of 22 kcal per kilogram of lean mass as a floor.
• Teens, pregnant, and breastfeeding women: a calorie deficit only with a registered dietitian and physician.

Setting a cut that drops your final number below those floors isn't an aggressive strategy. It's a method error. When your TDEE is too low to support the target, the move is to raise expenditure through NEAT and strength training, not to cut intake further.

Mistakes that erase the deficit by month's end

Forgetting liquid calories. Juice, soda, and coffee with milk add 200 to 500 kcal a day. People who log only solid food create a deficit on paper and hold weight in real life.

Eating "clean" 5 days and "free" 2 days. The week's balance is the average of 7 days. Two days with 800 extra kcal cancel out the deficit from the other five.

Not recalculating TDEE after losing 11 lb (5 kg). Every 11 lb lost drops your TDEE by 100 to 150 kcal. Keeping the same target after losing weight means slipping into maintenance without noticing. The plateau becomes a sentence instead of a warning.

Trusting the app without checking the portion. Most apps nail the intake math but miss the portion estimate when you just type "1 plate of food." Weighing once a week prevents silent error from piling up.

ContaCal: deficit calculated and balance measured on one screen

ContaCal is the photo-based calorie counting app that runs the TDEE math, sets the right cut for your goal, and hands back your daily target. Instead of logging every food by hand, you photograph the plate and the AI applies the step-by-step above.

To understand the link between TDEE and your daily calorie target in more depth, see the guide on how many calories you should eat. ContaCal automates the repetitive part and keeps the method consistent in the months when the early motivation fades.

📸 Camera instead of spreadsheet

From target to daily balance in seconds

In ContaCal, your deficit, your log, and your balance show up together so you can adjust the next meal.

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