Calorie Deficit Calculator

Calculator

How the daily target is calculated

Three steps, and none of them are hidden. First, your basal metabolic rate is estimated with the Mifflin–St Jeor equation: 10 × weight in kilograms, plus 6.25 × height in centimetres, minus 5 × age in years, then plus 5 for men or minus 161 for women. That is the energy your body uses at complete rest, and for most adults it accounts for somewhere between 60% and 70% of the day's total.

Second, that BMR is multiplied by an activity factor between 1.2 for a sedentary office life and 1.9 for a physical job or twice-daily training, giving your total daily energy expenditure. This is the honest weak point of every calculator of this kind: the multipliers are population averages, and for an individual the resulting TDEE carries an error band of roughly ten to fifteen per cent. On a 2,500 kcal estimate that is 300 kcal in either direction, which is larger than the deficit many people are trying to run. It is one reason the plan should be steered by what the scale does over a month, not by the arithmetic alone.

Third, the deficit itself. The weekly rate you pick is converted to a daily energy gap using the standard planning figure of 7,700 kcal per kilogram of body tissue: rate × 7,700 ÷ 7. A rate of 0.5 kg a week is 3,850 kcal over the week, or 550 kcal a day. Subtract that from your TDEE and you have the target, unless one of the rails in the next section moves it, in which case the result panel says which one and why.

Why we cap the rate

Faster than about 1% of bodyweight a week, the composition of what you lose deteriorates: more muscle and water, less fat. Hunger hormones surge, training quality drops, and adherence (the thing that actually determines outcomes) collapses. The research picture is consistent: moderate deficits with adequate protein preserve lean mass and are far more likely to stick. A 0.5% weekly rate feels slow on a chart and looks remarkable in a year.

The ~7,700 kcal per kilogram of body fat figure we use for planning is a decent long-run approximation, but real bodies adapt: expenditure drifts down as you get lighter, water masks fat on the scale for weeks at a time. Expect the line to wobble; judge by three-to-four-week averages.

The 1% ceiling is not arbitrary. Helms and colleagues, reviewing the evidence for natural bodybuilding contest preparation (the population with the strongest possible incentive to strip fat quickly and the strongest possible incentive to keep muscle while doing it), landed on 0.5 to 1% of bodyweight per week as the range that preserves lean mass. If that is the rate recommended to people whose livelihood depends on the outcome, it is a reasonable ceiling for everybody else.

The safety rails, in numbers

Four limits are written into the calculation layer of this site rather than into the advice around it, which means there is no combination of inputs that can talk the page past them. The weekly rate of loss cannot exceed 1% of your bodyweight. The daily target cannot fall below 80% of your TDEE. It cannot fall below 1,500 kcal for men or 1,200 kcal for women in absolute terms, whatever the percentage says. And a goal weight below a BMI of 18.5 for your height is refused outright, with the healthy range shown so you can pick a goal inside it.

Whichever rail binds first is the one that applies, and the result panel names it. A 60 kg woman asking for 0.75 kg a week hits the rate cap immediately, because 1% of her bodyweight is 0.6 kg. A sedentary person with a TDEE of 1,700 kcal asking for 0.5 kg a week hits the 80% rule, because the arithmetic wanted 1,150 kcal and 80% of 1,700 is 1,360. Someone smaller again may hit the absolute floor. In each case the number you are shown is the lowest target the page considers defensible, not the one the sum produced.

The floors are the same thresholds used in clinical practice to mark where intake stops being a self-managed diet and starts needing supervision. Very-low-energy diets below them exist and have a legitimate place, but their place is under a doctor or dietitian who can monitor electrolytes, medication and micronutrients, not behind a free web form that has never met you.

• Weekly rate: no faster than 1% of bodyweight a week.
• Relative floor: no lower than 80% of your estimated TDEE.
• Absolute floors: 1,500 kcal a day for men, 1,200 kcal a day for women.
• Goal weight: never below a BMI of 18.5 for your height.
• No countdown to a goal date, and no aggressive mode to switch any of it off.

Who should talk to a clinician before starting

Most healthy adults can run a moderate deficit without supervision. Several groups should not start one from a calculator, and the reasons differ enough to be worth listing rather than lumping into a disclaimer.

Pregnancy and breastfeeding are the clearest case: energy needs rise rather than fall, deliberate weight loss during pregnancy is not recommended, and the right tool is the pregnancy weight-gain guidance from your midwife or obstetrician. Anyone under 18 is blocked by this calculator outright: the adult equations are not valid for growing bodies, and a teenager wanting to change their weight deserves a conversation rather than a number. A history of an eating disorder is the group most poorly served by calorie targets in general: for some people a daily number is a useful structure and for others it is fuel, and only someone who knows your history can tell which.

Diabetes treated with insulin or sulfonylureas needs medical involvement because cutting carbohydrate and calories changes the dose required, and hypoglycaemia is a real and immediate risk rather than a theoretical one. The same applies to anyone on medication for blood pressure or a heart condition, where weight loss frequently means the dose needs revisiting. Adults over 65 lose muscle and bone faster in a deficit than younger adults do, so a slower rate, a higher protein intake and resistance training matter more, and an unplanned drop in weight at that age is itself worth investigating. And if weight is falling without you trying, a calorie target is the wrong response entirely: that is a symptom, and it needs a GP.

How to actually eat to the target

A target is a budget, not a schedule. Nothing in the arithmetic says when you eat, how many meals you have, or which foods are allowed; the number only says how much total energy the day can hold. Most people do best by anchoring protein first, because it is the macronutrient with a genuine floor and the one that protects lean mass, then building meals around a protein source, a large volume of vegetables, a carbohydrate portion sized to training, and fat for palatability and hormonal health.

Weigh food for a fortnight even if you never intend to keep doing it. Almost everyone misestimates portions of oils, nuts, cheese and sauces by a wide margin, and a short calibration period fixes the estimate permanently. After that, weighing the two or three highest-calorie items and eyeballing the rest is usually accurate enough, because the error on a plate of broccoli is not what closes a 500 kcal gap.

Volume is the other lever. At the same calories, a day built on lean protein, vegetables, fruit, legumes and whole grains is physically larger and takes longer to eat than one built on refined foods and liquid calories, and that difference is what makes a deficit survivable in month three. Drinks are the quiet failure mode: juice, soft drinks, alcohol and the milk in several coffees can account for a whole day's deficit without registering as food. And if your activity level here already includes your training, do not add exercise calories back on top: they are already counted, and tracker estimates of exercise burn run high, sometimes by thirty per cent or more.

• Set protein first, then fill the rest of the budget around it.
• Weigh food for two weeks to calibrate your eye, then weigh only the dense items.
• Choose high-volume, high-fibre foods so the same calories occupy more of the day.
• Count drinks, including alcohol, and do not eat exercise calories back if activity is already in your level.
• Keep the target the same on weekends: a large weekend routinely erases a week of weekday deficit.

What a stall actually is, and what to do about it

A stall is not a bad Tuesday. Body weight swings a kilogram or more on gut contents, sodium, glycogen, hydration and, for anyone who menstruates, the phase of the cycle, and those swings routinely hide two weeks of genuine fat loss. The definition worth using is two to three weeks of flat weekly averages, measured under the same conditions: same time of day, after the bathroom, before eating, on the same scale.

If the average really is flat, the arithmetic has drifted rather than failed. Two things cause it, and they usually happen together. Your TDEE is genuinely lower than it was, because you are carrying less mass and because the body reduces spontaneous movement in a deficit; and your intake has crept up, because portion estimates decay over time and bites, licks and tastes are not recorded by anyone. Neither is a moral failing, and neither is a reason to slash calories.

The fix in order of preference: re-run this calculator with your current weight, because the correct target shrinks as you do; add daily walking, which raises expenditure without eating into recovery; tighten measurement for a fortnight to recalibrate the estimate; and only then drop the target by 100–150 kcal. Never drop below the floors on this page. If several rounds of that produce nothing, a planned two-week break at maintenance is a legitimate move: adherence recovers, hormones normalise, and the subsequent deficit works better than the one you were failing to run.

Why there is deliberately no countdown to a goal date

Every ingredient for a date exists in this page: a starting weight, a goal weight and a planned weekly rate. Dividing one by the other takes a single line of code. We do not do it, and the omission is the point.

The date would be wrong, and wrong in a predictable direction. The 7,700 kcal per kilogram constant assumes the deficit stays constant and the body does not respond to it. Hall and colleagues, modelling the dynamics properly in the Lancet, showed that applying the static rule over a year predicts roughly twice the weight loss a dynamic model does, because expenditure falls as mass is lost and adaptation compounds month after month. A calculator that prints '18 March' is making a promise the physiology will not keep.

The behavioural cost is worse than the arithmetic error. A date turns a process into a deadline, and deadlines that pass unmet are the standard trigger for abandoning a plan that was in fact working, just more slowly than a spreadsheet said. Weight loss is not a countdown; it is a rate you maintain until you stop needing to. What this page gives you instead is the rate itself, the deficit in per-day, per-week and per-month terms, and a clear instruction to re-run it as your weight changes. Those are the numbers you can act on today, and they are still true next month.

How it's calculated

Worked example: a 35-year-old woman, 165 cm and 78 kg, lightly active, goal 68 kg

1. BMR by Mifflin–St Jeor: 10 × 78 + 6.25 × 165 − 5 × 35 − 161 = 780 + 1,031.25 − 175 − 161 = 1,475 kcal.
2. TDEE: 1,475 × 1.375 (lightly active) = 2,028 kcal a day, displayed rounded to 2,030.
3. Check the goal first: the healthy range for 165 cm is 18.5 × 1.65² = 50.4 kg to 24.9 × 1.65² = 67.8 kg. A goal of 68 kg sits just above the top of that range, so it is accepted: it is a step toward the range, not below it.
4. Chosen rate, 0.5 kg a week. Check the rate cap: 1% of 78 kg is 0.78 kg a week, so 0.5 passes through unchanged.
5. Daily deficit: 0.5 × 7,700 ÷ 7 = 3,850 ÷ 7 = 550 kcal.
6. Daily target: 2,028 − 550 = 1,478 kcal, displayed as 1,480.
7. Check the 80% rail: 80% of 2,028 is 1,623 kcal, and 1,478 is below it, so the rail binds, and the target is raised to 1,623 kcal, displayed as 1,620. The panel says the deficit was capped and why.
8. That leaves a real deficit of 2,030 − 1,620 = 410 kcal a day, which is 2,870 kcal a week and about 12,300 over 30 days, a genuine rate closer to 0.37 kg a week than the 0.5 requested.
9. Protein: 78 × 1.8 = 140 g to 78 × 2.2 = 172 g a day, which at four meals is roughly 35–43 g a meal.
10. No date is produced. Re-running the numbers at 74 kg will give a lower TDEE and therefore a lower target, which is exactly the point.

Where this number is used in the real world

• Everyday weight management, where the useful output is a number to eat to rather than a diet name to follow.
• Dietetic and general practice, as a transparent starting estimate that a clinician then adjusts for medication, comorbidity and preference.
• Sport with weight categories (combat sports, rowing, weightlifting), where fat has to come off across months without costing strength.
• Pre-operative weight loss programmes, where a modest supervised deficit is requested ahead of surgery and the arithmetic needs to be legible to both sides.
• Returning to a plan after a gaining phase, where knowing maintenance and a sane deficit prevents the usual overcorrection.
• Teaching and coaching, because the step-by-step arithmetic on this page shows exactly where each number comes from and what moves it.
• Sanity-checking an app's target, since many hand out numbers well below the floors used here without saying so.

Frequently asked questions

Keep going

A single number rarely tells the whole story. Alongside the calorie deficit result, the TDEE calculator, the macros calculator, the healthy weight range calculator, the protein calculator and the calorie surplus calculator each add a different angle on the same measurements. For the reasoning behind the numbers, read TDEE explained and Track without DEXA.

Sources

1. Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr 1990;51:241–7. doi.org/10.1093/ajcn/51.2.241
2. Wishnofsky M. Caloric equivalents of gained or lost weight. Am J Clin Nutr 1958;6:542–6. doi.org/10.1093/ajcn/6.5.542
3. Hall KD, Sacks G, Chandramohan D, et al. Quantification of the effect of energy imbalance on bodyweight. Lancet 2011;378:826–37. doi.org/10.1016/S0140-6736(11)60812-X
4. Helms ER, Aragon AA, Fitschen PJ. Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. J Int Soc Sports Nutr 2014;11:20. doi.org/10.1186/1550-2783-11-20
5. Morton RW, Murphy KT, McKellar SR, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. Br J Sports Med 2018;52:376–84. doi.org/10.1136/bjsports-2017-097608