Calorie Deficit Calculator: Find Your Fat Loss Calories
Work out how many calories you need to lose fat, without guessing. Enter your details to see your maintenance calories, a safe fat loss target, how fast you can expect to lose and how much protein to eat to keep your muscle.
Work out your fat loss calories
Enter your sex, age, height, weight and how active you are, then choose how fast you want to lose. It works in kilograms and centimetres, or pounds, feet and inches.
- Sex: male or female
- Age: 18 to 80
- Height: 140 to 220 cm
- Weight: 40 to 250 kg
- Activity level: sedentary, lightly active, moderately active, very active or extremely active
- Deficit: mild (10%), moderate (20%, recommended) or aggressive (25%)
| Result | Sample |
|---|---|
| Maintenance calories | 2,590 kcal (10,840 kJ) |
| Fat loss target | 2,070 kcal (8,660 kJ) |
| Estimated weekly loss | 0.4–0.55 kg |
| Daily protein | 170 g |
How a calorie deficit works
Your body burns energy all day: to keep you alive, to move you around and to digest your food. Add it up and you get your maintenance calories, also called your total daily energy expenditure (TDEE). Eat about that much and your weight stays roughly where it is.
Eat less than maintenance and you're in a calorie deficit. Your body makes up the gap from stored energy, and when the deficit is sensible and your protein is high, most of that comes from body fat.
A common rule of thumb is that a kilogram of body fat holds about 7,700 kcal. Treat it as an estimate, not a law: fat tissue holds some water, and your body adapts a little as you lose weight. It's still useful for planning. A 500 kcal daily deficit adds up to 3,500 kcal a week, or roughly 0.45 kg of fat.
Fat loss isn't a straight line on the scales. Water, glycogen (the carbs stored in your muscles), a salty restaurant meal or a big training week can move your weight by a kilogram overnight. That's why you judge progress on a weekly average, not a single weigh-in.
Protein and strength training matter more in a deficit, not less. They tell your body to hold on to muscle, so the weight you lose is mostly fat and you finish leaner, not just smaller.
How this calculator works
It starts with the Mifflin-St Jeor equation, one of the most widely used formulas for estimating your basal metabolic rate (BMR): the calories you burn at rest.
- Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
- Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
- Maintenance = BMR × your activity level: 1.2 sedentary, 1.375 lightly active, 1.55 moderately active, 1.725 very active, 1.9 extremely active
- Mild deficit: 10% below maintenance, about 0.25 kg a week for most men
- Moderate deficit (recommended): 20% below maintenance
- Aggressive deficit: 25% below maintenance
Your target never drops below your BMR, or below 1,500 kcal for men and 1,200 kcal for women, whichever is higher. Weekly loss is also capped at about 1% of your bodyweight. If one of these limits kicks in, the calculator tells you.
Protein is set the same way as in our macro calculator: about 2.55 g per kg of estimated lean mass for men and 2.25 g for women. For most men that lands around 1.8 g per kg of bodyweight, and it keeps heavier people from getting a number they can't realistically eat.
Every result is an estimate. Eat to your target for two to three weeks, track your weekly average weight, and adjust by 100–200 kcal if the trend isn't moving.
Worked example: a 40-year-old busy professional
Take a 40-year-old man who is 180 cm tall, weighs 95 kg and is lightly active: a desk job and two or three gym sessions a week.
- BMR = 10 × 95 + 6.25 × 180 − 5 × 40 + 5 = 1,880 kcal
- Maintenance = 1,880 × 1.375 = about 2,585 kcal (shown as 2,590)
- Moderate deficit (20%) = about 2,070 kcal a day, a deficit of about 517 kcal
- Estimated loss = 517 × 7 ÷ 7,700 = about 0.47 kg a week, shown as 0.4–0.55 kg
- Mild (10%) = about 2,330 kcal, around 0.25 kg a week
- Aggressive (25%) = about 1,940 kcal, around 0.6 kg a week, still above his BMR
- Protein = about 170 g a day
What 2,070 kcal looks like on a busy day
His day starts with a 6 am session, runs into back-to-back meetings, includes a client lunch at a place he didn't pick, and ends with either a late flight home or the school pick-up. Here's a sample day that fits around all of that at about 2,070 kcal and 166 g of protein.
| When | What | Calories | Protein |
|---|---|---|---|
| After the 6 am session | 250 g plain high-protein Greek yoghurt, 100 g mixed berries, 30 g untoasted muesli | 310 kcal | 30 g |
| Between meetings | A regular flat white | 130 kcal | 7 g |
| Client lunch | 200 g grilled lean steak, a big side salad with dressing, a small serve of roast potatoes | 650 kcal | 60 g |
| Afternoon | Protein shake (30 g whey in water) and a banana | 220 kcal | 25 g |
| Dinner, at home or after the flight | 180 g salmon, 150 g cooked rice, steamed vegetables, 1 tsp olive oil | 660 kcal | 43 g |
| Evening | Two squares of dark chocolate | 100 kcal | 1 g |
| Total | 2,070 kcal | 166 g |
The numbers are approximate and vary by brand and portion. What matters is the shape of the day: protein at every meal, a lunch you can order almost anywhere, and room for something you enjoy.
If the flight runs late and dinner is airport food, pick the meal with the most protein and skip the extras you wouldn't usually eat. One off-plan meal doesn't undo a week.
Common calorie deficit mistakes
Cutting too hard
A huge deficit feels productive for a week. Then hunger, poor sleep and flat training sessions catch up, and most people who start that way end up back at maintenance within a month.
Forgetting liquid calories and alcohol
Client dinners, a few beers on the weekend and milky coffees add up fast. Alcohol carries 7 kcal per gram, and it usually brings food with it.
Underestimating the weekend
Five careful days and two loose ones can wipe out the whole week's deficit. Look at your weekly total, not just your weekdays.
Eating back all your exercise calories
Watches and gym machines tend to overestimate what you burn. Your activity level is already in your maintenance number, so you don't need to add it again.
Low protein and no strength training
Without both, a good share of the weight you lose can be muscle. That leaves you smaller but no leaner, and it lowers how much you burn each day.
Judging progress on daily weigh-ins
Your daily weight jumps around with water and salt. Weigh in most mornings and compare weekly averages instead.
Never recalculating
As you lose weight, your maintenance drops with it. Rerun your numbers every 4–5 kg, or whenever your weekly average stalls for three weeks.
Blaming starvation mode
Your metabolism doesn't shut down in a sensible deficit. It does adapt a little, and most people move less without noticing, which is why recalculating and keeping your daily steps up both matter.
Calorie deficit FAQs
How big should my calorie deficit be?
For most men, 15–25% below maintenance works well, which is usually 400–700 kcal a day. Our moderate setting uses 20%. That's big enough to see steady progress and small enough to keep training well, sleeping properly and sticking with it for months. If you have a lot to lose you can push a little harder early on. If you're already lean, go gentler.
How fast will I lose weight in a calorie deficit?
About 0.5–1% of your bodyweight a week is a sensible pace, so roughly 0.45–0.9 kg a week for a 90 kg man. Expect a bigger drop in the first week or two as water and stored carbs come off, then a slower, steadier trend. Judge the pace on your weekly average over three or four weeks, not on one weigh-in.
Is a 1,000-calorie deficit safe?
For most people it's too aggressive to hold. Unless your maintenance is very high, a 1,000 kcal deficit pushes you towards or below your BMR, which usually costs muscle, energy, sleep and training quality. This calculator stops your target at your BMR, at 1,500 kcal for men or 1,200 kcal for women, and at about 1% of your bodyweight a week. Get medical advice before going further.
Should I eat back the calories I burn exercising?
Usually not. Your activity level is already built into your maintenance calories, so eating back what a watch or treadmill says you burned counts the same exercise twice, and those devices tend to overestimate. If you do a big one-off session, like a long hike or a half marathon, a little extra food that day is fine.
Why am I not losing weight in a calorie deficit?
Most of the time the deficit is smaller than you think. Common causes are untracked weekend meals, alcohol, cooking oils and sauces, and portions that creep up over time. Water retention from stress, poor sleep, salty food or a new training program can also hide fat loss for a week or two. If your weekly average hasn't moved in three weeks, drop your target by 100–200 kcal.
Can I build muscle in a calorie deficit?
Yes, especially if you're new to lifting, coming back after a break or carrying more body fat. Eat enough protein, keep the deficit moderate and train with weights three or four times a week, pushing a little harder over time. Experienced, lean lifters will mostly hold their muscle rather than add it, which is still a win while you lose fat.
Do I have to count calories forever?
No. Counting for a few months teaches you what portions look like and where your calories come from. After that, most people keep their results with simpler habits: protein at every meal, a regular weigh-in and a quick check when the trend drifts. A coach can help you make that switch without losing what you've built.
Next steps
Once you have your calories, split them into protein, carbs and fat with our free macro calculator. If you'd rather have a coach adjust your numbers every week, around work and travel, take the 2-minute quiz or book a call with Ryan.
Built by Ryan Spiteri, NewU head coach. Last reviewed October 2026.
This calculator gives general estimates for healthy adults and isn't medical advice. If you're pregnant or breastfeeding, under 18, have a medical condition or a history of disordered eating, talk to your GP or an Accredited Practising Dietitian before changing how you eat.