Calorie Deficit Calculator: Work Out Your Real Numbers
Almost every weight loss plan you have been sold is a repackaging of one number: the gap between what you eat and what you burn. Everything else - the meal timing, the lemon water, the fasting window, the twelve-week challenge - is a strategy for hitting that gap or a distraction from it. This page gives you the number, explains where it comes from, and is honest about what it cannot tell you.
Enter your details below. Nothing is stored, nothing is sent anywhere, and there is no email gate. Then read the rest of the article, because a calorie target you do not understand is a calorie target you will abandon in three weeks.
Your details
The equation uses this because average lean mass differs. Pick whichever matches your physiology.
Metabolic rate falls roughly 5 kcal per year of age
Be honest here. Overstating activity is the single most common reason a deficit does not work.
Anything above 1% of body weight a week starts costing you muscle rather than fat.
Eat this many calories a day
1,580
calories per day
That is a deficit of 550 calories a day against your maintenance of 2,130.
1,549
BMR
at complete rest
2,130
Maintenance (TDEE)
to stay the same
10 kg
to lose
from 82 kg to 72 kg
23 wks
realistic timeline
20 weeks on paper
BMI now
29.1
Overweight
BMI at target
25.5
Overweight
A starting macro split
Protein is set at 1.8 g per kg of your target weight - high enough to protect muscle while you are in a deficit. Fat sits at 25% of intake; carbohydrate takes the balance.
130g
Protein
520 kcal
44g
Fat
396 kcal
166g
Carbs
664 kcal
What that deficit looks like on a plate
About 550 calories a day is roughly 3 festivals. You do not have to cut those specific things - it is just a sense of scale. Most people find it easier to remove one drink and one fried side than to overhaul every meal.
Eating in a deficit costs less, not more
Last Bite lets you buy surplus food from local restaurants and bakeries at up to 70% off. Smaller portions, lower cost, nothing thrown away.
Method: Mifflin-St Jeor equation for BMR, Harris-Benedict activity multipliers for TDEE, 7,700 kcal per kg of body fat for the projection. Timelines re-estimate maintenance at your target weight, which is why the realistic figure is longer than the on-paper one. This tool is general information, not medical advice. If you are pregnant, breastfeeding, under 18, or managing diabetes, heart disease or an eating disorder, speak to a doctor or registered dietitian before changing your intake. Nothing you enter is stored or sent anywhere.
The three numbers behind your target
1. Basal metabolic rate
Your BMR is what your body burns doing nothing at all - keeping your heart beating, your lungs working, your kidneys filtering and your body at temperature. If you lay perfectly still in a dark room for twenty-four hours, this is the bill. For most adults it accounts for between 55 and 70 per cent of daily energy use, which is why the popular idea that exercise is the main lever is wrong. Your body burns most of its fuel just being alive.
We calculate it with the Mifflin-St Jeor equation. It has been the recommended formula since a systematic review by the American Dietetic Association in 2005 found it more accurate than the older Harris-Benedict equation across both lean and heavier adults. The maths is unglamorous:
2. Total daily energy expenditure
Nobody lies still in a dark room. TDEE is your BMR multiplied by an activity factor that accounts for everything else - walking, working, fidgeting, training, digesting. The multipliers run from 1.2 for a genuinely sedentary life to 1.9 for hard physical labour or two training sessions a day.
This is the step where most people go wrong, and it is worth being blunt about it. Almost everyone selects one notch too high. Three gym sessions a week does not make you very active if the remaining hundred and sixty-five hours are spent sitting in a car, at a desk and on a sofa. If your calculated target is not producing results after a month of honest eating, the activity multiplier is the first thing to lower - not the calories.
| Activity level | Multiplier | What it actually looks like |
|---|---|---|
| Sedentary | 1.2 | Desk job, drive everywhere, under 5,000 steps a day |
| Lightly active | 1.375 | Exercise 1-3 days a week, some walking, 5,000-7,500 steps |
| Moderately active | 1.55 | Exercise 3-5 days a week, or on your feet most of the working day |
| Very active | 1.725 | Hard exercise 6-7 days a week, or a physical trade |
| Extremely active | 1.9 | Two sessions a day, farm or construction labour, competitive athlete |
3. The deficit
A kilogram of body fat stores roughly 7,700 calories - the figure comes from a 1958 paper by Max Wishnofsky and has survived as the standard planning number ever since. Divide by seven and you get the daily gap needed for a given weekly rate:
| Weekly loss | Daily deficit | Suits |
|---|---|---|
| 0.25 kg (0.5 lb) | ~275 kcal | Anyone already close to goal, or protecting hard-won muscle |
| 0.5 kg (1.1 lb) | ~550 kcal | The default. Visible progress, sustainable for months |
| 0.75 kg (1.7 lb) | ~825 kcal | Higher starting weight, short defined push |
| 1 kg (2.2 lb) | ~1,100 kcal | Only sensible above roughly 100 kg, and not for long |
Why the honest timeline is longer than the arithmetic one
Here is the part most calculators quietly skip. Divide the weight you want to lose by your weekly rate and you get a clean answer: 10 kg at 0.5 kg a week is twenty weeks. That answer is wrong, and predictably so.
Maintenance calories are a function of body mass. An 82 kg person burns more at rest than the same person at 72 kg - about 100 calories a day more, in the equation above. So a fixed calorie target that starts as a 550 calorie deficit is only a 450 calorie deficit by the time you are most of the way there. The gap closes as you approach the goal, which is exactly why progress feels like it stalls in the final stretch even when nothing about your behaviour has changed.
The calculator handles this by re-estimating your maintenance at your target weight and averaging the two, which is why it reports a realistic timeline alongside the on-paper one. The realistic figure is typically 10 to 20 per cent longer. Knowing that in advance is the difference between adjusting and quitting.
What the calculator cannot tell you
Every prediction equation is a population average applied to an individual, and individuals vary. Two people of identical height, weight, age and sex can have maintenance needs differing by 200 to 300 calories a day. The reasons include thyroid function, medication, sleep quality, gut microbiome, past dieting history and how much you unconsciously move - a trait researchers call non-exercise activity thermogenesis, which varies enormously between people and falls when you diet.
So treat the output as a starting hypothesis, not a verdict. Eat at the target for a fortnight, weigh yourself under the same conditions, and compare the weekly average. If you have lost the predicted amount, the estimate was good. If nothing has moved after two clean weeks, cut 150 calories or add a daily walk. If you are losing faster than 1 per cent of body weight a week, eat more.
The floors, and why they exist
The calculator will not set a target below 1,200 calories for women or 1,500 for men. This is not squeamishness. Below those levels it becomes genuinely difficult to hit protein, iron, calcium, iodine and B-vitamin requirements from food, and micronutrient deficiency is a real cost that does not show up on a scale. A larger share of the weight lost also comes from lean tissue, which lowers your maintenance further and makes the weight easier to regain.
There is a second, less discussed cost. Very aggressive deficits have poor adherence. A plan you abandon in five weeks loses less weight than a slower plan you keep for six months, even though the aggressive plan looks better on a spreadsheet. The best deficit is the largest one you can actually live with, which for most people is smaller than the one they first choose.
Protein is the one macro worth being strict about
In a deficit your body will take some energy from muscle unless you give it reasons not to. Two things prevent that: enough protein, and resistance training. The calculator sets protein at 1.8 grams per kilogram of your target weight, which sits in the range most reviews of the evidence support for people losing weight.
In Jamaican terms that is easier than the supplement industry implies. A tin of mackerel, a piece of chicken, a serving of red peas, two eggs and a portion of saltfish will comfortably clear the target without a scoop of imported powder. We costed the cheapest options in a separate piece on high-protein meals; the short answer is that chicken back, mackerel and red peas beat everything else per dollar.
How to run this in practice
- Get the number. Use the calculator, take the target and write it down. Do not adjust it for the first two weeks.
- Track honestly for two weeks. Weigh food if you can, estimate if you cannot, but count the drinks, the oil in the pan and the piece you ate standing at the counter. Untracked calories are the single biggest reason a correct target appears to fail.
- Weigh weekly, same conditions. Morning, after the bathroom, before eating, same day of the week. Compare weekly averages rather than individual readings.
- Adjust once a month, by one lever at a time. Either 150 calories off intake or a daily twenty-minute walk on. Changing three things at once tells you nothing about which one worked.
- Recalculate every 5 kg. Your maintenance has moved. So should your target.
Frequently asked questions
How do I work out my caloric deficit?
Estimate your basal metabolic rate with the Mifflin-St Jeor equation, multiply by an activity factor to get maintenance calories, then subtract the gap you want. A kilogram of body fat holds roughly 7,700 calories, so a 550 calorie daily deficit predicts about half a kilogram a week. The calculator on this page does all of it from your gender, age, height, current weight, target weight and activity level.
What is a safe rate of weight loss?
Between 0.5 and 1 per cent of body weight per week. For an 82 kg adult that is roughly 0.4 to 0.8 kg a week. Faster than 1 per cent and a growing share of what you lose is muscle and water rather than fat, and the weight comes back more easily.
Why did I stop losing weight in a deficit?
Three usual causes, in order of likelihood. First, intake has drifted upward without you noticing, because portions grow and untracked extras add up. Second, your maintenance has fallen, since a lighter body burns less and a fixed calorie target therefore produces a smaller deficit over time. Third, water retention is masking real fat loss, which is common after a hard training session, a salty meal or during the luteal phase of the menstrual cycle.
Do I have to count calories forever?
No. Most people count carefully for four to six weeks, which is long enough to learn what portions of their own regular meals actually look like, then switch to checking occasionally. The point of tracking is calibration, not permanent bookkeeping.
Can I lose weight eating Jamaican food?
Yes. The dishes are not the problem. What blows the daily budget is usually fried sides, sweet drinks and portion size. Roast or boiled provisions instead of fried, water or unsweetened tea instead of a box drink, and one scoop of rice instead of three will move most people into a deficit without changing what they cook.
Is BMI useful?
It is a rough screening tool, not a diagnosis. It says nothing about body composition, so a muscular person can read as overweight and a sedentary person with little muscle can read as healthy. Use it as one number among several, alongside waist measurement and how your clothes fit.
Sources
- Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition, 1990.
- Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults. Journal of the American Dietetic Association, 2005.
- Wishnofsky M. Caloric equivalents of gained or lost weight. American Journal of Clinical Nutrition, 1958.
- NHS - Start losing weight and calorie counting guidance
- World Health Organization - Healthy diet fact sheet
