What is a calorie deficit?

A calorie deficit means eating fewer calories than your body burns (your TDEE). When you do, your body makes up the difference by using stored fat for energy, and you lose weight. It is the fundamental mechanism behind all fat loss.

How big should my calorie deficit be?

A deficit of 300-500 calories per day suits most people, producing about 0.25-0.5 kg (0.5-1 lb) of fat loss per week. Aggressive deficits above 750-1000 kcal accelerate muscle loss and hunger and are harder to sustain. A safe target keeps daily intake at or above your BMR.

How long will it take to lose the weight?

Roughly 7,700 calories equals 1 kg of body fat (3,500 per pound). Divide the total weight you want to lose by your weekly deficit to estimate the timeline. The calculator above does this for you and flags if your chosen rate is too aggressive.

Why is my weight loss slowing down?

As you lose weight your TDEE falls, so the same intake becomes a smaller deficit. You also lose water early on, which exaggerates the first weeks. Recalculate every 4-5 kg and adjust your calories down to keep the deficit consistent.

Is 1200 calories a safe deficit?

1,200 calories is a floor, not a goal. Eating well below your BMR for long periods can cost you muscle and harm hormones. This calculator never recommends below 1,200 kcal and warns if your target approaches your BMR.

Free Calorie Deficit Calculator — Calories & Timeline to Your Goal Weight

Biological sex

Age

Height

Current weight (kg)

Goal weight (kg)

Target rate of loss

Activity level

Maintenance (TDEE)

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kcal / day

What you burn at current weight

Total to lose

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Time to goal

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weeks

Want your full macro breakdown at this target?

Protein matters most in a deficit — it protects muscle while you lose fat. Get your protein, carb, and fat split for these calories with the Macro Calculator → or set protein alone with the Protein Calculator →

Stay in your deficit, day after day

Knowing the number is easy — hitting it daily is the hard part. NutriBalance logs meals by barcode scan or AI food photo and shows your remaining calories in real time, with streaks and weekly leagues to keep you consistent. 14-day free trial, no card required.

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How it works

The maths behind your deficit

A calorie deficit is eating less than your body burns. This tool first estimates your maintenance calories (TDEE, via Mifflin-St Jeor), subtracts the deficit implied by your chosen weekly rate, then estimates how long the journey takes using the energy content of body fat.

Step 1 — Daily deficit from your target rate

About 7,700 kcal is stored in 1 kg of body fat (≈ 3,500 kcal per pound).

Daily deficit = (weekly kg × 7,700) ÷ 7. So 0.5 kg/week ≈ a 550 kcal/day deficit.

Step 2 — Your calorie target

Target calories = TDEE − daily deficit, with a hard floor at 1,200 kcal and a warning if it dips near your BMR.

Step 3 — Estimated timeline

Weeks to goal = total kg to lose ÷ weekly rate. Real-world loss isn't perfectly linear — water shifts and a falling TDEE mean you should recalculate every 4–5 kg.

FAQ

Frequently asked questions

It's eating fewer calories than your body uses in a day. When intake is below your TDEE, your body covers the gap by burning stored fat — and you lose weight. Every diet that works, regardless of its name, ultimately creates a calorie deficit. The size of the deficit sets how fast you lose.

For most people, 300–550 kcal/day (about 0.25–0.5 kg per week) is the sweet spot — fast enough to stay motivating, gentle enough to protect muscle and sanity. Very large deficits accelerate muscle loss, spike hunger, and tank adherence. Keep daily intake at or above your BMR.

Divide the weight you want to lose by your weekly rate. At 0.5 kg/week, losing 10 kg takes roughly 20 weeks. The calculator gives you a specific estimate and date. Expect faster loss in the first couple of weeks (water) and a gradual slowdown as your body gets lighter and your TDEE drops.

As you lose weight, your TDEE falls, so the calories that once created a deficit may now be your new maintenance. Day-to-day water fluctuations also mask fat loss. Recalculate your deficit every 4–5 kg, stay consistent for at least 2–3 weeks before judging, and trust the longer-term trend over the daily scale.

Track your intake. You can't stay in a deficit you can't see. NutriBalance shows your remaining calories in real time as you log meals by barcode scan, AI food photo, or search — and keeps you accountable with streaks and weekly leagues so the habit sticks long enough to reach your goal.

Calorie Deficit Calculator