Why this exists
Almost every keto calculator online does the same thing: takes your maintenance calories, slices off a fixed percentage for carbs, another for protein, and calls the rest fat. It looks scientific and it is backwards. Ketosis responds to the absolute grams of carbohydrate you eat, not to the share of your plate they occupy, so deriving carbs from a percentage hands a large man twice the carbohydrate of a small woman and calls both of them ketogenic.
The second reason is the first fortnight. Everyone loses a lot of weight in week one on keto and most of it is the water bound to glycogen. Every calculator we looked at either ignores this or mentions it once in a footnote. It is the single most common reason people misread their own progress, either declaring victory too early or quitting in week three when the water has gone and the real rate appears. We put a number on it and draw it.
Who writes it
A small independent team that builds calculators. None of us holds a clinical qualification, and you will not find a stock photograph of a doctor with a tick next to it anywhere on this site. That pattern is everywhere in health content and it is worth almost nothing, because nobody can verify the reviewer or what they actually reviewed.
Instead, every equation is named on the homepage with its source, and the parts we constructed ourselves are labelled as ours. If you disagree with a number you can go and check it, which is a better guarantee than a name you cannot audit. Corrections are genuinely welcome at hello@ketocalculator.co.uk.
What we are confident about
- Nutritional ketosis begins at a blood beta-hydroxybutyrate of 0.5 mmol/L, and 20 to 50 g of net carbs a day is the range that produces it. This is consistent across the entire literature.
- Glycogen is stored with water, and losing it accounts for most of week one on the scale. The mechanism is not in dispute.
- Gluconeogenesis is demand-driven. Eating more protein does not reliably end ketosis, and the moderate-protein convention costs people lean tissue for a reason that does not hold up.
- At matched calories and protein, keto does not out-perform other diets for fat loss. Its real advantage is appetite suppression, which is worth having but is not what most keto marketing claims.
- Keto flu is sodium and potassium depletion, and salting your food properly prevents most of it.
What is genuinely uncertain, and we say so on the page
- The water-per-gram-of-glycogen ratio. The classic figure is 3 grams of water per gram of glycogen, from Olsson and Saltin in 1970. More recent work argues the real ratio is lower and more variable. We publish a range rather than a point, and the range is wide on purpose.
- The protein interpolation. The research gives a band of 2.3 to 3.1 g per kg of lean mass and an instruction that leaner people should sit higher in it. The exact curve we use between those two numbers is our own construction. It is a defensible reading, not a published equation.
- Where your personal carb ceiling sits. Nobody can calculate this. A muscular person who trains hard may hold ketosis at 50 g; a sedentary person may not hold it at 30. Only a blood meter will tell you.
- The fat mobilisation ceiling. The 48 kcal per kg of fat mass figure is derived from Alpert's modelling work, corrected for a unit error that circulates widely online. Alpert's published figure is per pound, and the frequently quoted per-kilogram version is a factor of 2.2 too small. We use the conservative corrected value, and it is a model rather than a measurement.
- Activity multipliers. They are conventions. Being one tier out is worth several hundred calories a day, which is more than most of the precision elsewhere on the page is worth.
Safety
This is information, not medical advice, and there are three situations where you genuinely should not act on it without speaking to your doctor first.
- SGLT2 inhibitors. Dapagliflozin, empagliflozin and canagliflozin combined with very low carbohydrate have produced ketoacidosis at normal blood glucose, which is dangerous precisely because your sugars look reassuring. There are multiple published case reports of exactly this combination.
- Insulin or sulfonylureas. Cutting carbohydrate sharply while your dose stays the same is a straightforward route to a hypo. Doses usually need reducing within days.
- Kidney disease, liver disease, pancreatitis, pregnancy, or a history of disordered eating. Each of these changes the calculation in ways no web page can account for.
The calculator will also refuse to hand you a target below the greater of the usual 1,200 or 1,500 calorie guideline and 30 calories per kilogram of lean mass, and it says so when it raises your number. Keto suppresses appetite well enough that people undereat by accident, which is exactly why that floor is there.
Privacy
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