Calculate your daily calorie and macro targets for a ketogenic (very low-carb, high-fat) diet.
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The ketogenic diet is a very low-carbohydrate, high-fat eating plan designed to shift the body into ketosis, where fat becomes the primary fuel source instead of carbohydrates. A standard keto macro split is roughly 70% fat, 25% protein, and only about 5% carbohydrates (typically under 20-50g of net carbs per day). This calculator estimates your daily calorie needs using the Mifflin-St Jeor equation, then splits those calories into keto-friendly macro targets to help you plan meals that keep you within ketosis. The diet restricts carbs to typically under 50 grams of net carbs daily, deliberately depleting glycogen stores to force a metabolic shift toward burning fat for fuel. Once glycogen is low enough, the liver converts fats into molecules called ketones, which most body tissues — including a large portion of the brain — can use as an alternative energy source, a metabolic state known as nutritional ketosis.
The ketogenic diet's defining feature is severe carbohydrate restriction — typically under 50 grams of net carbs daily, sometimes lower — designed to deplete the body's glycogen stores and force a metabolic shift toward burning fat for fuel. When carbohydrate intake drops low enough, the liver begins converting fatty acids into ketone bodies, which can cross the blood-brain barrier and serve as an alternative fuel source for the brain, which otherwise relies almost exclusively on glucose. This state, called ketosis, typically takes 2-4 days of strict carbohydrate restriction to reach, though the timeline varies by individual.
This calculator's macro split — a fixed 70% fat, 25% protein, and 5% carbohydrate — reflects the ratios most commonly used to reliably maintain ketosis, since even moderate carbohydrate intake can interrupt the metabolic shift for many people. Protein is deliberately kept moderate rather than high, because excess protein can be converted into glucose through a process called gluconeogenesis, which can slow or prevent ketosis if protein intake runs too high relative to fat and carbohydrate.
The diet originated in the 1920s as a medically supervised treatment for drug-resistant epilepsy, particularly in children, and remains in clinical use for that purpose today under medical supervision. Its more recent popularity for weight loss and general health is supported by a growing (though still developing) body of research showing benefits for some markers of metabolic health and short-to-medium-term weight loss, though long-term studies comparing it directly against other dietary approaches remain more limited than for many other popular diets.
The initial adjustment period, sometimes called "keto flu," commonly involves fatigue, headache, and irritability as the body adapts to a new primary fuel source and electrolyte balance shifts — adequate sodium, potassium, and magnesium intake during this transition meaningfully reduces these symptoms for most people. As with any restrictive eating pattern, consulting a doctor before starting is particularly important for anyone with existing kidney issues, a history of disordered eating, or who is on medication for diabetes, since the metabolic shift can significantly affect blood sugar and requires medication adjustment in some cases.
Most people aim for 20-50g of net carbohydrates per day to stay in ketosis, though this varies by individual.
Yes, it's common in the first few days — fatigue, headache, and irritability as the body adapts to burning fat instead of glucose — and usually resolves within a week as the body adjusts.
Keto is not recommended for people with certain conditions such as pancreatitis, liver disease, or a history of eating disorders — consult a doctor before starting any restrictive diet.