Keto Calculator

Keto Macros Calculator

Net carbs as a hard limit, protein sized to your lean mass, fat filling what is left. Then the part other calculators leave out: how much of your first week is water, and how much is actually fat.

Your details

−30% cut+10% gain

Why use this keto calculator

Net carbs are a limit, not a percentage

Every other calculator derives your carbs from a 5% slice of your calories, which means a 110 kg man is told he can eat twice the carbohydrate of a 55 kg woman. Ketosis does not work that way. You pick the gram target, and everything else is built around it.

It separates the water from the fat

The first week on keto empties your glycogen, and every gram of glycogen leaves with three grams of water. We estimate the parcel, subtract it, and draw both lines so you can see what actually came off. This is why keto feels like a miracle on day five and a failure on day twelve.

Protein sized to protect muscle

Keto's blind spot. The convention is moderate protein, based on a gluconeogenesis worry the evidence does not support, and the cost is lean tissue. Your starting target is scaled to lean mass and rises as you get leaner. Drag it down to the classic range if you want, and the page will tell you what that costs.

It tells you how to read the packet

On a UK or EU label the Carbohydrate line already excludes fibre, so it is net carbs and you subtract nothing. American labels include it, which is why most keto advice tells you to subtract. Getting that backwards costs you part of your allowance every day, and no other calculator mentions it.

Electrolytes on the results page

Most people who quit in week one quit because of something a teaspoon of salt would have fixed. Keto flu is sodium and potassium leaving, not detox. You get the actual milligram targets, not a vague nudge to drink more water.

No account, no upsell, nothing to buy

No email capture, no custom keto plan for £27, no exogenous ketone affiliate links. It runs entirely in your browser and nothing you type ever leaves your device.

How it works

  1. 1

    Tell us about yourself

    Age, height, weight and how active you are. Kilos or pounds, whichever you think in, and we show the stone conversion either way.

  2. 2

    Pick the range that looks like you

    Six ranges with a description each, or give us a scan figure or three tape measurements. Most people have never had a scan, and a description you can recognise in the mirror beats a formula that cannot tell muscle from fat. It sets your lean mass, and your lean mass sets your protein.

  3. 3

    Set your calorie adjustment

    One slider, from a thirty percent deficit to a ten percent surplus. It explains what each level means as you move it, and it will refuse to hand you a deficit your fat stores cannot fund.

  4. 4

    Then adjust the split yourself

    Two more sliders sit on the results: net carbs in grams, and protein per kilo of lean mass. Fat absorbs the difference and the pie redraws as you drag. Below that, what the scale will do week by week, when ketosis arrives, and how much salt you need to get there without a headache.

Who this is for

Starting keto this week
You want a number to eat to, and you would rather not find out about keto flu the hard way. Start at 20 g, read the electrolyte table before day two, and expect the scale to lie to you for a fortnight.
Two weeks in and the scale has stopped
It has not stopped. The water left, and what you are seeing now is the actual rate. The chart shows exactly this shape, which is usually enough to stop people abandoning something that is working.
Lifting and worried about losing muscle
A reasonable worry, and mostly a protein problem rather than a carbohydrate one. Use the higher protein setting and watch what happens to the lean tissue line in the projection.
Coming back to keto after a break
Glycogen refilled while you were off, so the week-one drop happens again, and it is water again. Knowing that in advance saves you drawing the wrong conclusion in either direction.
On medication for type 2 diabetes
Read the medication warning at the bottom of your results before you change anything. SGLT2 inhibitors plus very low carbohydrate has caused ketoacidosis at normal blood sugar, and insulin doses usually need cutting within days. This is a conversation with your doctor, not a web page.

What a keto calculator is actually working out

Four numbers, in a specific order, and the order is the part most tools get wrong.

A ketogenic diet is defined by one thing: eating little enough carbohydrate that your liver starts producing ketone bodies in quantity. Everything else follows from that. So the sum begins with calories, fixes carbohydrate as a hard gram limit, sets protein from your lean mass, and lets fat take whatever is left over.

Read that back and notice what is missing. Nowhere did anyone decide the diet should be 75% fat. That figure is a result, and it moves depending on your size, your goal and how big a deficit you are running. When a calculator opens by declaring 75/20/5 and works backwards to grams, it produces carbohydrate targets that scale with bodyweight, which is nonsense: ketosis responds to the absolute grams you eat, not to the fraction of your plate they represent.

A worked example of the problem. Take a 5% carbohydrate rule. A 55 kg woman eating 1,500 calories gets 19 g of carbs and lands in ketosis. A 110 kg man eating 3,000 gets 38 g and may well not. Same rule, opposite outcomes, and neither of them was ever asked what they wanted.

The three numbers, ranked by how much they matter

1. Net carbs. This one is a wall.

Below roughly 50 g a day, and reliably below 20 g, your liver runs out of glucose to distribute and starts converting fatty acids into ketone bodies. Blood beta-hydroxybutyrate crossing 0.5 mmol/L is the accepted definition of nutritional ketosis, and most people get there on day two to four. This is the only number in the whole plan that behaves like a genuine threshold. Miss it and you are on a low-carb diet, which is a perfectly good diet, but it is not the one you came for.

2. Protein. Chase this one upwards.

Keto's inherited wisdom is moderate protein, on the grounds that surplus amino acids get converted to glucose and knock you out of ketosis. The mechanism is real but the direction of causation is not: gluconeogenesis is demand-driven, your liver produces the glucose your body requests rather than manufacturing more because supply turned up. What is real is arithmetic. Carbs are capped and calories are fixed, so every gram of protein you add is a gram of fat you have to remove. Protein and fat are competing for one budget, and this calculator shows you when the fight is getting tight.

3. Fat. This one is a remainder.

Fat fills the gap, which makes it a ceiling with a floor underneath rather than a target to hit. Eating fat is not what causes ketosis; not eating carbohydrate is. If you come in a little under on a day you were not hungry, you have simply run a slightly larger deficit, and if the goal is fat loss that is not a problem. This is where the butter-in-coffee era went wrong: people treated a remainder as a quota and added several hundred uncounted calories a day to hit it.

Why your fat percentage will read lower than 75%

If you are eating in a deficit, your calculated split will probably come out somewhere around 60 to 68% fat rather than the textbook 75%. Nothing is broken. The textbook figure describes someone eating at maintenance, where every calorie arrives on a plate.

In a deficit, part of your fuel comes off your own body, and body fat is pure fat. Someone eating 1,800 calories at 62% fat with a 600 calorie deficit is actually running on 2,400 calories of fuel, of which 1,716 are fat. That is 71%. Their metabolism has no idea which fat arrived by fork. This calculator shows you both figures, because the dietary one is what you shop for and the effective one is what your liver responds to.

Net carbs on a food label

Net carbs are the carbohydrate your body can actually use. How you read that off a packet depends on where the packet was printed, and most keto advice online assumes American labelling without saying so.

LabelThe Carbohydrate line meansWhat you do
UK and EU Available carbohydrate, fibre already excluded and listed separately underneath Nothing. Take the number as it stands.
United States Total carbohydrate, calculated by subtraction, fibre included in the figure Subtract the fibre line to get net carbs

UK and EU labelling defines carbohydrate as the part that is actually metabolised. Fibre sits beneath it as of which fibre and is not counted in the headline number. So when a keto blog tells you to subtract fibre from total carbs, and you do that to a Sainsbury's label, you are subtracting fibre that was never in there in the first place.

Sugar alcohols are the messier case. Erythritol is essentially not metabolised and can be discounted; maltitol raises blood glucose enough that discounting it will get you into trouble. Polyols appear inside the carbohydrate figure, so if a product leans on maltitol, count it.

The first two weeks, without the mythology

Your muscles and liver store carbohydrate as glycogen, and glycogen is stored wet: roughly three grams of water for every gram of glycogen. Stop eating carbohydrate and that entire parcel is released over about a week. For most adults it is one and a half to three kilos.

This produces the single most predictable emotional arc in dieting. Week one is spectacular. Week two looks like a stall. Neither is true. The rate you see from week three onwards is the real one, and it was always the real one. It also means the weight comes straight back the first time you eat a proper plate of pasta, which is not a relapse, it is a tank refilling.

The honest comparison. When trials match calories and protein, ketogenic diets do not produce more fat loss than other diets. The advantage keto genuinely has is appetite: most people eat less on it without trying, and a deficit you can actually hold beats a theoretically superior one you abandon in March. That is a real benefit. It is just not a metabolic one, and anyone telling you carbohydrate itself makes you fat is selling something.

Keto flu is a salt problem

Headache, fatigue, cramp, fog and a short fuse, usually days two to seven. It is not your body detoxing from sugar. When insulin falls, your kidneys stop retaining sodium and begin excreting it, and potassium follows. The symptoms are those of mild dehydration and low sodium, because that is what they are.

The clinical group with the most published ketogenic practice puts the targets at 3,000 to 5,000 mg of sodium a day, which is around 8 to 12 g of table salt, alongside 3,000 to 4,700 mg of potassium and 300 to 500 mg of magnesium. Those figures sit well above general population advice, deliberately, because the general population is not running on low insulin. Salt your food properly, drink a mug of stock in the afternoon of day two, and most of week one simply does not happen.

One exception worth taking seriously: if you have high blood pressure, heart failure or kidney disease, do not adopt a 5,000 mg sodium target from a website. Ask your doctor what your number should be.

Methodology

There is no reviewer byline on this page, because inventing a doctor to put a photograph next to would be worth less than showing the working. Here is every equation the calculator uses and where it comes from.

StepWhat we useSource
Resting metabolic rate Mifflin-St Jeor by default; Katch-McArdle when you supply a measured body fat percentage and your BMI is 30 or below Mifflin et al. 1990; Katch-McArdle / revised Cunningham 1991
Maintenance calories Resting rate multiplied by a five-step activity factor, 1.2 to 1.9 Conventional activity multipliers. Broad steps, not measurements
Body fat from tape US Navy circumference method, imperial regressions, all inputs converted to inches Hodgdon and Beckett 1984. Accurate to about 3 to 4 percentage points
Body fat without tape Deurenberg BMI equation. Cannot distinguish muscle from fat, so it over-reads on lifters Deurenberg, Weststrate and Seidell 1991
Protein, higher setting 2.3 to 3.1 g per kg of lean mass in a deficit, rising as body fat falls Helms et al. 2014, adopted verbatim by the ISSN protein position stand. The curve between those two bounds is our interpolation, not a published formula.
Protein, classic setting 1.2 to 1.7 g per kg of lean mass, scaled by activity Conventional ketogenic practice. Offered because people running therapeutic protocols want it, not because we think it is optimal
Deficit ceiling About 48 kcal per kg of fat mass per day, capped again at 1,000 kcal Derived from Alpert's fat mobilisation work, corrected for the unit error that circulates widely. Alpert's figure is per pound, not per kilogram
Calorie floor The greater of 1,200 (women) / 1,500 (men) and 30 kcal per kg of lean mass 2013 AHA/ACC/TOS prescription range, and the RED-S energy availability threshold. The second is the better grounded of the two
Glycogen water 13 g of glycogen per kg of lean mass, about 60% of it lost, each gram carrying 3 g of water Olsson and Saltin 1970 for the water ratio. Shown as a range because the ratio is contested and recent work argues it is lower.
Energy density 7,700 kcal per kg of adipose tissue; 4/4/9 kcal per gram for carbohydrate, protein and fat Standard constants. The 7,700 figure is a population average, not your personal exchange rate
Ketosis threshold Blood beta-hydroxybutyrate at or above 0.5 mmol/L, with 0.5 to 3.0 covering nutritional ketosis Standard clinical definition, consistent across the ketogenic literature

What this calculator cannot tell you

  • Whether you personally will hold ketosis at 30 or 40 g. Nobody can predict that. It depends on muscle mass, training volume and adaptation. Only a blood ketone meter answers it.
  • Your true maintenance calories. Any equation plus an activity multiplier will be a few hundred calories out. Eat to the number for three weeks, track your average weekly weight, and correct from what actually happened. That correction beats every formula on this page.
  • Whether keto is the right diet for you. It is very good at controlling appetite and very awkward around social eating, endurance training and vegetarian cooking. The best diet is the one still running in six months.
  • How your medication will respond. This is the one that can genuinely hurt you. SGLT2 inhibitors combined with very low carbohydrate have produced ketoacidosis while blood glucose looked normal, and insulin or sulfonylurea doses usually need reducing within days of cutting carbs. Speak to your doctor or diabetes team first.

Keto questions, answered properly

How do I work out my macros for keto?
In this order, and the order is the whole trick. Work out maintenance calories from your resting rate and activity, then adjust for your goal. Fix net carbs as a hard number, usually 20 to 50 g. Set protein from your lean mass, not your total weight. Then fat fills whatever calories are left. Notice that fat is the last thing decided, never the first. Any calculator that starts by declaring 75% fat is running the sum backwards and will hand a 60 kg woman and a 110 kg man the same shaped plan.
What is the ideal macro ratio for keto?
There is not one, and the famous 70/25/5 is a description rather than a prescription. It is roughly what the numbers land on when someone of average size eats at maintenance with carbs capped. Change the size or the goal and the percentages move on their own. In a deficit your fat percentage will read lower, because a chunk of your fuel is coming off your waist instead of off your plate. Count that in and the ratio your body is actually running looks very close to the textbook figure. Ketosis is caused by restricting carbohydrate, not by hitting a fat percentage.
What is the 2-2-2-2 rule on keto?
It is a community slogan, not a clinical protocol, and it has no single agreed meaning. The most common version is a two-week adaptation pattern: two tablespoons of MCT oil, two of another fat, two servings of non-starchy veg, for two weeks. A competing version reads it as macro targets: 2 g of protein per kg, 2 g of fat per kg, under 20 g of net carbs, 2 litres of water. Neither has been tested. The MCT version in particular adds several hundred uncounted calories a day, which is a good way to stall. Your actual carbohydrate, protein and fat totals matter more than any rhyme.
How many carbs a day can I eat and stay in ketosis?
Somewhere between 20 and 50 g of net carbs for most people, and where you personally sit inside that is genuinely individual. Muscle mass, training volume and how long you have been keto-adapted all move it, because a well-trained person can bury a surprising amount of carbohydrate in muscle glycogen without touching blood ketones. 20 g is the reliable starting point, the level at which almost everyone reaches ketosis. Once you are established, work upwards in 5 g steps and let your ketone readings tell you where your own ceiling is rather than guessing from a blog.
Do I count net carbs or total carbs?
It depends on where the label was printed, which almost nobody tells you. On a UK or EU label the line marked Carbohydrate is already net carbs: it declares available carbohydrate only, with fibre listed separately underneath as of which fibre. Take that number straight off the packet and subtract nothing. American labels are built the other way round, their Total Carbohydrate includes fibre, which is why most keto advice online tells you to subtract. Follow that on a Tesco label and you will quietly under-count your allowance every single day.
Will too much protein kick me out of ketosis?
Almost certainly not, and this is the most persistent myth in the whole area. The worry is that surplus protein is converted to glucose by gluconeogenesis. Gluconeogenesis is real, but it is demand-driven rather than supply-driven: your liver makes the glucose your body asks for, it does not manufacture more simply because more amino acids turned up. Studies feeding large protein loads to people in ketosis do not show the collapse in ketones the theory predicts. The genuine constraint is arithmetic, not metabolic. On a fixed calorie budget with carbs capped, every gram of protein is a gram of fat you cannot eat, so protein and fat compete for the same space.
How much weight will I lose on keto?
In week one, more than you have lost fat, and it is worth knowing why before you get attached to the number. Cutting carbohydrate drains muscle and liver glycogen, and every gram of glycogen is stored with roughly three grams of water. For most adults that is one and a half to three kilos of water leaving in the first week or so. After that, fat loss runs at the same pace it would on any other diet with the same calorie deficit, because it is the deficit doing the work. Head-to-head trials that match calories and protein find keto has no fat-loss advantage. What it does have is appetite suppression, which makes the deficit easier to hold, and that is a real advantage even if it is not a metabolic one.
How long does it take to get into ketosis?
Two to four days for most people. Glycogen runs down over the first 24 to 72 hours, and blood beta-hydroxybutyrate typically crosses 0.5 mmol/L, the accepted threshold for nutritional ketosis, somewhere on day two to four. Being in ketosis and being adapted to it are different things though. Adaptation takes three to four weeks, and that is when training performance comes back, appetite settles, and the whole thing stops feeling like an endurance test. Fasting or hard training gets you there faster; a slack first week gets you there not at all.
What is keto flu, and how do I avoid it?
Headache, fatigue, brain fog, cramp, and a short temper, usually days two to seven. It is not detox and it is not your body complaining about missing carbohydrate. It is salt and water. When insulin falls, your kidneys stop holding on to sodium and start dumping it, and potassium goes out with it. The fix is unglamorous: 3,000 to 5,000 mg of sodium a day, which is about 8 to 12 g of table salt, plus potassium from avocado and leafy greens and 300 to 500 mg of magnesium. Salt your food properly and drink stock. Most people who quit keto in week one quit because of something a teaspoon of salt would have prevented. If you have high blood pressure, heart failure or kidney disease, check that sodium figure with your doctor first.
Are keto macros different for women?
The equations are the same, with two adjustments that matter. Resting metabolic rate is calculated with a different constant for women, so the calorie target is lower for the same height and weight. And the body fat percentages are not comparable: essential fat is around 13% for women against 5% for men, and a healthy range sits roughly ten points higher throughout. That shifts the protein calculation too, because protein is scaled to lean mass and to leanness. Beyond the arithmetic, women on very low calories are more likely to run into menstrual disruption, which is why this calculator refuses to go below 30 calories per kilogram of lean mass no matter what you ask it for.
Do I have to hit my fat target exactly?
No, and treating it as a target you must reach is how people end up eating butter out of a mug. Fat is the remainder in this calculation, which makes it a ceiling with a floor under it rather than a bullseye. Come in a bit under on a day you are not hungry and you have simply run a slightly larger deficit, which is fine if you are losing fat. Carbohydrate is the only number that behaves like a hard limit, because it is the one that decides whether you are in ketosis at all. Protein is the one worth chasing upwards. Fat is what fills the gap.
How do I know I am actually in ketosis?
A blood ketone meter is the only measurement worth much. Nutritional ketosis is 0.5 mmol/L and up, with 0.5 to 3.0 covering everything a person eating for weight loss needs; the deeper range above that belongs to therapeutic epilepsy protocols and is not a better result. Urine strips are cheap and fine for the first fortnight, then they mislead you, because once adapted you waste fewer ketones and the strips fade even as ketosis deepens. Breath meters sit in between. Honestly, though, once you are a month in the readings stop being useful. If your carbs are genuinely capped, you are in ketosis, and the scale and the tape tell you the thing you actually wanted to know.