Calorie Deficit Calculator

Your maintenance calories and the daily target for the pace you choose — by the US government’s 2023 equations and by the one every other calculator uses, side by side, because they disagree. It will not plan a crash: the pace stops at 2 lb a week and the target stops at the floor a doctor would draw.

You are

The equations were published separately for each sex; there is no third set to offer.

years
ft in
lb

Type the unit if it is easier — 82 kg, 178 cm, 12 st 12 — and the toggle follows you.

How active are you?

You want to
How fast?

lb

Adds how many weeks it takes at this pace — and says so if the target is under a healthy weight for your height.

Eat this many calories a day

1,755 calories a day

This is arithmetic, not medical advice, and it is for adults who are not pregnant or breastfeeding. Any equation is a starting point: weigh yourself for two or three weeks, then adjust by what actually happens. If you have a health condition, or a history of an eating disorder, plan this with a doctor or a registered dietitian instead.

Equations and guidance checked 2026-09-23.

Quick answer: to lose about a pound a week you eat roughly 500 calories a day below what you burn; for two pounds a week, about 1,000. What you burn is the part nobody can look up — it depends on your size, age and movement — so the calculator works it out two ways and shows you both. Public-health guidance puts the sensible pace at 1 to 2 pounds a week, and the floor for dieting without a doctor at 1,200 calories a day for women and 1,500 for men. This tool will not go past either.

How to use it

Put in your age, height and weight — type the units if it is quicker, 82 kg or 5’6″ or 12 st 12, and the toggle will follow you. Pick the activity level that matches an ordinary week, not your best one. Then choose a pace. The big number is what to eat; underneath it are your maintenance calories, your resting rate, the size of the deficit and your BMI.

Add a goal weight and it also tells you roughly how many weeks that takes — and says so plainly if the goal is below a healthy weight for your height, in which case it will not plan towards it.

Why the page gives you two numbers

Because two respectable methods disagree, and every other calculator quietly picks one.

The National Academies’ 2023 equations

In 2023 the National Academies of Sciences, Engineering, and Medicine published new Dietary Reference Intakes for Energy. Their equations predict total daily energy expenditure straight from age, height, weight and activity category, and they were fitted to doubly-labelled-water data — a method that measures what people actually burn while living their normal lives, rather than inferring it from a resting measurement in a laboratory. This is the official US answer, and it is the headline here.

Mifflin-St Jeor, times an activity factor

This is what nearly every calorie calculator on the internet does: estimate your resting metabolic rate with the Mifflin-St Jeor equation, published in 1990 and the best-validated of the classic formulas, then multiply by 1.2 for a desk job, 1.375 for light activity, and so on. The resting half is solid. The multiplying half is a convention — no official body publishes those factors — which is worth knowing when a calculator presents the result to the calorie.

The two often differ by a few hundred calories, and part of the reason is worth knowing: the 2023 categories are bands of physical activity level — “inactive” covers everything from 1.0 to 1.53 — while an activity factor is a single number. We map the conventional factors onto the report’s four bands so the answers can sit side by side, and a band is wider than a multiplier. The page prints the gap, because that gap is the honest width of any calorie estimate. We do not average them: the midpoint would be a number nobody published.

What the caps are, and why they are not negotiable here

This site is called BurnMyFatFast, so it is worth being blunt: the tool will not help you go faster than the evidence supports.

  • Two pounds a week is the ceiling. The CDC describes 1 to 2 pounds a week as the pace people are most likely to keep off. Ask for more and the tool holds at two and says so.
  • 1,200 calories for a woman, 1,500 for a man is the floor. That is Harvard Health’s line for dieting without medical supervision. If your goal needs less than that, the tool keeps the floor and moves the date instead — which is the same answer, honestly stated.
  • It will not plan towards an underweight goal. Type a goal weight below a BMI of 18.5 for your height and the calculator stops and says where the healthy range starts.
  • It is for adults who are not pregnant or breastfeeding. Under 18, calorie needs and a healthy weight are worked out by percentile instead; the CDC has the right tool and a doctor is the right person.

Why the weight loss slows down even when you do not

The arithmetic behind every deficit calculator is the old rule that a pound of body fat is worth about 3,500 calories. It is a decent approximation for the first few weeks and it drifts afterwards, because a lighter body burns fewer calories doing the same things. In 2011 a team led by Kevin Hall published the replacement in The Lancet: for an average adult with overweight, a permanent change of 10 calories a day leads to about a pound of eventual change, with half of it arriving after roughly a year and 95% after about three.

The practical version: the plate that produced a pound a week in January produces less than that by April, at the same discipline. That is not failure, and it is not your metabolism breaking. It is arithmetic, and the fix is to re-run this page at your new weight every ten pounds or so.

Getting the activity level right

This is where most people overshoot, and it is the input with the biggest effect on the answer. The categories come from the 2023 report and are defined by physical activity level — total energy burned divided by resting energy. “Inactive” is a desk job with no deliberate exercise. “Lightly active” is roughly half an hour to forty minutes of moderate movement a day on top of ordinary life. “Active” is an hour of real exercise most days, or physical work. “Very active” is an athlete’s week, or heavy manual labour. Three gym sessions a week is usually “lightly active”, not “active” — and a week you had once is not the week to put in.

FAQ

How many calories should I eat to lose weight?
Take what you burn in a day and subtract about 500 for a pound a week, or 1,000 for two. The number to subtract from is personal: this calculator works it out from your age, sex, height, weight and activity by two published methods and shows both. What it will not do is take you below 1,200 calories a day if you are a woman or 1,500 if you are a man — that is the line Harvard Health draws for dieting without medical supervision.
Is a 1,200 calorie diet safe?
It is the floor rather than a target, and it is the floor precisely because going below it makes it hard to get enough protein, calcium, iron and the rest. Plenty of people eat at 1,200 for a while under supervision; the problem is arriving there by accident because a calculator handed you the number. If your goal needs less than the floor, the honest answer is a longer timeline, more movement, or a conversation with a dietitian.
Why is my calculated maintenance different from my fitness tracker’s?
A tracker counts your steps and heart rate and adds them to an estimate; these equations start from measurements of total energy use in people living normally. Both are estimates with error bars of a few hundred calories, and trackers are known to be generous with exercise burn. Use either as a starting point, weigh yourself over two or three weeks, and let your own trend correct the number — that measurement beats every equation on this page.
What is the difference between BMR and maintenance calories?
Your BMR — basal or resting metabolic rate — is what you would burn lying perfectly still for 24 hours, and it is usually 60-70% of the total. Maintenance is everything: resting, moving, fidgeting, digesting and exercising. You eat against maintenance, not against BMR, and eating at your BMR is nearly always too little.
Can I lose 10 pounds in a month?
Ten pounds in a month is 2.5 pounds a week, which is above the range public-health guidance describes and above what this tool will plan. Some of it would be water rather than fat, especially in the first fortnight and especially if you cut carbohydrate. At two pounds a week — the top of the range — ten pounds takes about five weeks, and you will still be able to eat enough to train and to sleep.
Do I need to eat back the calories I burn exercising?
Not with this tool. The activity level you choose already includes your exercise, so the target below is what to eat on an ordinary week — training included. Adding an exercise burn on top of it counts the same movement twice, which is the most common way people end up eating at maintenance while believing they are in a deficit.
Why does the calculator refuse my goal weight?
Because it is below a BMI of 18.5 for your height, which is where the healthy range starts. That is a published cut-off, not a judgement about you, and the page shows the weight where the range begins. If a target under it feels necessary, that is a conversation worth having with a doctor or a registered dietitian rather than with a calculator.