A calorie deficit is the engine of every fat-loss plan. Figure out the right size for you, hold it consistently, and the scale moves. This tutorial walks you through the math in five minutes.
Quick Answer
Deficit = TDEE − target intake
For most adults:
- −250 to −500 kcal/day → moderate, sustainable loss (~0.25–0.5 kg/week)
- −500 to −750 kcal/day → faster loss for higher-body-fat starters
- Floor: 1,200 kcal/day for women, 1,500 kcal/day for men without supervision
Use our Calorie Calculator (pick "Lose weight") to get the number directly.
Step 1: Find Your TDEE
TDEE is the calorie level that holds your weight steady today.
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Compute BMR with our BMR Calculator.
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Multiply by an activity factor:
| Lifestyle | Multiplier | |---|---| | Sedentary | 1.2 | | Lightly active | 1.375 | | Moderately active | 1.55 | | Very active | 1.725 |
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Or skip to our TDEE Calculator.
Example: a 70 kg, 30-year-old man, moderately active → BMR 1,649 × 1.55 ≈ TDEE 2,556 kcal.
Step 2: Choose a Deficit Size
The right deficit scales with how much body fat you carry.
| Body-fat range | Suggested deficit | |---|---| | Very lean (men under 12%, women under 20%) | 200–400 kcal/day | | Moderate | 400–700 kcal/day | | Higher body fat | 600–1,000 kcal/day |
The cutter above with moderate body fat: pick −500 kcal/day → target intake 2,056 kcal.
A reasonable rule of thumb: 0.5–1% of body weight per week is a sustainable rate of loss for most people.
Step 3: Translate to Macros
Lock protein first to preserve muscle:
- 1.8–2.2 g per kg body weight during a cut
- 70 kg cutter at 2.0 g/kg → 140 g protein (560 kcal)
Then fat:
- 0.6–1.0 g/kg — say 0.8 → 56 g fat (504 kcal)
Carbs fill the rest:
- 2,056 − 560 − 504 = 992 → 992 / 4 = 248 g carbs
Run the split automatically with our Macro Calculator.
Step 4: Project the Weight Change
One kilogram of body fat ≈ 7,700 kcal. So:
Weekly loss (kg) ≈ (daily deficit × 7) / 7,700
For our −500/day cutter: 3,500 / 7,700 ≈ 0.45 kg/week.
Predictions are 70–90% of actual loss because metabolism adapts. Expect drift; plan to adjust.
Reading the Scale Honestly
The single most common reason people abandon a working calorie deficit is misreading short-term scale noise as failure. Daily body weight fluctuates by 1–2 kg or more from water, glycogen, food in transit, and salt timing — none of which is fat.
Three principles that separate signal from noise:
- Weigh every morning (after the bathroom, before food/drink, naked or in the same clothes). Same conditions = comparable data.
- Compare 7-day averages, not single days. A 0.4 kg drop in this week's average vs. last week's average is real progress; a 0.4 kg drop overnight is nothing.
- Ignore single-day spikes of up to 1.5 kg after high-carb or salty meals. They are water, not fat. They normalise within 24–72 hours.
For women, track across full menstrual cycles. Water retention in the luteal phase can mask 1–3 weeks of real fat loss; the drop usually shows up sharply after menses.
Refeeds and Diet Breaks During a Cut
Longer cuts benefit from planned interruptions to the deficit:
- Refeed day — one day per week at maintenance calories, with the extra calories coming primarily from carbs (250–400 g for a 70 kg lifter). Protein stays the same. Restores muscle glycogen, lifts training quality, and gives a mental break without sabotaging the average weekly deficit.
- Diet break — a full 7–14 days at maintenance every 8–12 weeks of cutting. Used in long cuts to reset hormones (leptin, thyroid) and refresh adherence.
Refeeds and diet breaks slow the cut on paper but often speed it in practice because adherence stays high. Cutters who refuse them tend to plateau and abandon the diet entirely.
Step 5: Adjust Based on Real Data
After 2–3 weeks of consistent execution:
- Weight trend matches prediction → keep going
- Loss is slower than predicted → drop intake another ~10% (or add 4,000 daily steps)
- Loss is faster than predicted (and you feel terrible) → add 100–200 kcal back
- Scale stalled but waist is shrinking → trust the tape over the scale
The adjustment loop is what separates plans that work from plans that don't.
When the Cut Should End
Cuts have a natural lifespan. Pushing past it almost always costs more than it gains. Stop the cut and return to maintenance when:
- Body fat has reached your target (typically 10–15% for men, 18–22% for women)
- You have been in a deficit for 12+ weeks without a structured diet break
- Strength has dropped on multiple lifts for 3+ consecutive weeks
- Sleep, mood or libido have deteriorated noticeably
- Resting heart rate has fallen 10+ bpm below your normal baseline
- Body temperature feels chronically cold, especially in the hands and feet
These are the body's signals that adaptation has taken over and the deficit is starting to extract a tax. Coming out cleanly — via reverse dieting, adding 50–100 kcal/week until you reach the new maintenance — preserves the result.
A cut that ends well is more valuable than a cut that pushes one more kilogram. The plan after the cut is what determines whether the result lasts.
Common Mistakes
- Picking a deficit by feel. "Around 1,500 kcal" without knowing TDEE is guessing.
- Eating back exercise calories on top of an active multiplier. Double-counting flattens results.
- Going too aggressive. A 1,000+ kcal deficit shreds adherence and muscle.
- Forgetting protein in the deficit. Lower protein = more muscle lost per kg of weight loss.
- Re-tracking only one bad day. Average across the week; one snapshot rarely matters.
Frequently Asked Questions
How fast can I safely lose weight?
For most adults, 0.5–1% of body weight per week is a sustainable target. Faster losses cost more muscle and adherence, and the bigger calorie deficit makes nutrient sufficiency harder.
Should I eat back the calories my watch says I burned?
Be cautious — wearables typically over-estimate burn by 20–30%. If your activity multiplier already reflects training, don't add tracker calories on top.
What about diet breaks?
A 1–2 week diet break at maintenance every 8–12 weeks of cutting often improves long-term adherence and metabolic response without much delaying total fat loss.
Can I create the deficit just by exercising more?
You can, but the bigger lever for most people is food intake. A 500 kcal/day exercise increase is roughly an extra 75 minutes of running per day — not realistic for most. A 500 kcal food reduction is one less large meal.
Is a 1,200 kcal day safe?
It can be on the low edge of safety for sedentary smaller adults; for taller or active people it's usually too low. Floor without medical supervision is 1,200 kcal/day for women and 1,500 kcal/day for men.
Bottom Line
The math is honestly small:
- Find TDEE → TDEE Calculator.
- Pick a deficit (250–700 kcal/day depending on body fat).
- Lock protein → Macro Calculator.
- Hold for 2–3 weeks, average the scale.
- Adjust by 10% if reality and prediction disagree.
The hard part is not the calculation — it's the consistency. The calculation just makes sure you're consistent at a number that actually works.
Health and fitness calculations are estimates only and not medical advice. Anyone with eating disorder history, diabetes, pregnancy, or chronic conditions should plan a cut with a healthcare provider or registered dietitian.