How big should a calorie deficit be to lose weight safely?

A deficit of about 300–700 kcal per day suits most people. A larger deficit is acceptable if you carry more body fat (higher BMI), while leaner people should keep it modest to protect muscle. Aim to lose roughly 0.5–1% of your body weight per week.

Will I lose weight just by eating fewer calories?

A calorie deficit is what drives fat loss, but how you eat matters. Enough protein (1.6–2.2 g/kg) and some resistance training preserve muscle, so most of the weight you lose is fat rather than muscle. Without them, a deficit can cost you muscle and slow your metabolism.

Do I need to count calories forever?

No. Counting is a learning tool. After a few weeks you will recognise portion sizes and can switch to lighter tracking. A photo calorie app removes most of the friction, so you can log a meal in seconds while you build the habit.

Nutrition

How Many Calories Should I Eat to Lose Weight?

Q: How many calories should I eat to lose weight?

Estimate your TDEE (the calories you burn per day) and eat below it. A safe deficit is roughly 15–25% under TDEE, depending on how much fat you have to lose. For many adults that lands between 1,400 and 2,000 kcal per day. Never eat below your BMR for long periods.

📅 3 June 2026⏱ 9 min read

TL;DR

The rule: eat fewer calories than you burn (a calorie deficit) — everything else is detail
Find your number: BMR → TDEE → subtract 15–25%
Safe rate: lose 0.5–1% of body weight per week (≈ 0.4–0.8 kg for an 80 kg person)
Protect muscle: 1.6–2.2 g/kg protein + 2–3 strength sessions a week
Floor: don’t sit below your BMR for long stretches

1) Weight loss in one sentence

You lose weight when you eat fewer calories than your body uses over time. That gap is called a calorie deficit. Diets get marketed as keto, fasting, low-carb, “clean eating” — but every one of them only works if it puts you in a deficit. So the real question isn’t “which diet?”, it’s “how many calories should I eat?” Let’s get you a number.

2) Find your maintenance calories (TDEE)

Your TDEE (total daily energy expenditure) is the calories you burn in a day. Eat at TDEE and your weight stays flat; eat below it and you lose fat. Two quick steps:

Step 1 — BMR (calories at rest)

The Mifflin-St Jeor equation is the modern standard:

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

Don’t fancy the maths? Use the free BMR calculator — it does this in one tap.

Step 2 — Multiply by your activity level → TDEE

Activity level	Multiplier
Sedentary (desk job, little exercise)	1.2
Lightly active (1–3 days/week)	1.375
Moderately active (3–5 days/week)	1.55
Very active (6–7 days/week)	1.725

→ Skip the maths: Free Calorie Calculator

3) Set your deficit (this is your fat-loss number)

Subtract a percentage of your TDEE. How much depends on how much fat you have to lose — leaner people should be gentler to protect muscle, while those carrying more body fat can take a slightly larger cut. This is the same BMI-aware logic KeplerFit uses inside the app:

Your situation (BMI)	Suggested deficit
Lean (BMI under 25)	TDEE − 12% to 15%
Overweight (BMI 25–30)	TDEE − 18%
Higher body fat (BMI 30+)	TDEE − 20% to 22%

Safety floor: never park below your BMR for weeks on end. Very low intakes wreck energy, sleep and adherence — and you lose muscle, not just fat. A modest deficit you can sustain beats an aggressive one you quit.

4) Worked example: 80 kg, 178 cm, 32-year-old man, lightly active

Step	Calculation	Result
BMR	10×80 + 6.25×178 − 5×32 + 5	≈ 1,757 kcal
TDEE	1,757 × 1.375	≈ 2,416 kcal
Deficit (−18%)	2,416 × 0.82	≈ 1,981 kcal

Daily target ≈ 1,980 kcal. At that intake he’d lose roughly 0.5–0.7 kg per week — steady, sustainable, and muscle-sparing. Run your own numbers with the calorie calculator and check your starting point with the BMI calculator.

5) How fast should weight come off?

Aim for 0.5–1% of your body weight per week. Faster than that and you start losing muscle and water weight that bounces straight back. The scale also lies day to day — water, sodium, glycogen and your cycle move it by 1–2 kg overnight. Judge progress on the weekly average, not a single morning.

6) A deficit alone isn’t a plan

Here’s where most calorie counters stop — and where people stall. A number on its own doesn’t tell you why your progress slowed. The three things that decide whether the weight you lose is fat or muscle:

Protein: 1.6–2.2 g/kg keeps you full and protects muscle in a deficit.
Resistance training: 2–3 sessions a week tells your body to keep the muscle.
Consistency: hitting your target 6 days out of 7 beats a “perfect” day followed by a blowout.

This is exactly what KeplerFit watches for you. Instead of a static number, it tracks your weight trend, protein and training over the week and tells you what’s actually blocking progress — “your deficit is fine, but protein was low on 4 days, so cut the snack, not the calories.” That’s the difference between a tracker and a coach. See it in the app →

Muscle-Sparing Fat-Loss Circuit (No Equipment)

Pair your deficit with this 6-move home circuit, 3 rounds. Keeps muscle while you cut.

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🏠 Full-body circuit (home)

Compound moves that burn calories and protect muscle. Rest 45–60 sec between rounds.

Squat3×15

Push-up3×10

Lunge3×10

Glute Bridge3×15

Dead Bug3×10

Jumping Jack3×45 sec

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