Last updated: May 2026

CICO Calculator: How to Use Calories In Calories Out for Weight Loss

CICO stands for Calories In, Calories Out — the foundational principle behind every diet that has ever produced fat loss. It is not a specific diet plan. It is the mechanism by which all diet plans work. If you consume fewer calories than you burn, you lose weight. If you consume more, you gain. The challenge is calculating the “out” side accurately.

How CICO Works

Your body requires a certain number of calories each day to power all its functions — breathing, pumping blood, digesting food, walking, and exercising. This total is your TDEE (Total Daily Energy Expenditure). When your calorie intake matches your TDEE, your weight stays stable.

A calorie deficit — consuming less than your TDEE — forces your body to use stored energy (primarily body fat) to make up the shortfall. A 500-calorie daily deficit corresponds to approximately 1 pound of fat loss per week, since roughly 3,500 calories equals one pound of stored fat.

A calorie surplus — consuming more than your TDEE — results in stored energy, which is weight gain. Whether that stored energy becomes muscle or fat depends on the surplus size, training stimulus, and protein intake.

Step 1: Find Your Calories Out (TDEE)

Your TDEE is the cornerstone of CICO. It is calculated from your basal metabolic rate (the calories you burn at rest) multiplied by an activity factor.

The Mifflin-St Jeor equation gives your BMR:

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

Then multiply by your activity factor (1.2 sedentary → 1.9 very active) to get TDEE. Use the calculator above to skip the manual steps.

Step 2: Set Your Calorie Deficit

Once you have your TDEE, subtract calories to create the deficit:

A 500-calorie daily deficit is the most commonly recommended starting point. It produces steady results without the hunger, muscle loss, and hormonal disruption that come with severe restriction. Most people should not eat below 1,200 calories (women) or 1,500 calories (men) regardless of their deficit calculation.

Step 3: Understand Where Calories Come From

All calories come from three macronutrients. Understanding caloric density per gram helps with food choices:

Protein’s high thermic effect means your body uses 20–30% of protein calories just to digest it — so 100 calories of protein yields only 70–80 net calories. This is one reason high-protein diets support fat loss beyond the satiety benefit.

Step 4: Track Calories In

Accurately tracking food intake is the hardest part of CICO for most people. Common tools:

• Food tracking apps (MyFitnessPal, Cronometer): Scan barcodes, search food databases, log portions. The most accurate method for people new to CICO.
• Kitchen scale: Weighing food in grams removes the guesswork from portion sizes. Volume measurements (cups, tablespoons) are unreliable for calorie-dense foods like oils and nuts.
• Macro targets: Rather than tracking every calorie precisely, some people set daily protein, carbohydrate, and fat targets that indirectly control calories.

Studies consistently show that people who self-report food intake underestimate consumption by 20–50%. A kitchen scale and a tracking app together eliminate most of this error.

Common CICO Mistakes

Overestimating calories burned

Fitness trackers overestimate calorie burn by 20–30% on average. Using exercise as justification to eat more calories than were actually burned is the most common reason CICO “doesn’t work” for people — they are in a smaller deficit than they think, or no deficit at all.

Not accounting for liquid calories

Beverages — including coffee drinks, juice, sports drinks, alcohol, and smoothies — contain calories that are easy to forget. A single large latte with whole milk can be 250+ calories. These add up quickly against a 500-calorie deficit.

Eating at BMR instead of TDEE

BMR is your calorie burn at complete rest. Eating at BMR is not a mild deficit — it is aggressive restriction that creates muscle loss and metabolic adaptation. Always create your deficit from TDEE, not BMR.

How to Adjust When CICO Stalls

Fat loss plateaus are expected. As you lose weight, your TDEE drops because your body weighs less and often becomes more metabolically efficient. When fat loss stalls:

1. Recalculate TDEE at your new bodyweight. A 10 lb loss lowers TDEE by roughly 80–100 calories.
2. Check tracking accuracy. Portion creep — slightly larger servings than tracked — accumulates over time and can erase a deficit entirely.
3. Reduce intake by 100–200 calories and reassess over 2–3 weeks before making further changes.
4. Consider increasing NEAT rather than reducing food further. An extra 2,000 steps per day burns ~100 calories without touching food intake.