🍞Carbohydrate Calculator

Our carbohydrate calculator uses the Mifflin-St Jeor equation to estimate your Total Daily Energy Expenditure (TDEE) based on age, gender, height, weight, and activity level, then applies your target carbohydrate percentage to calculate daily carb grams. The calculator provides recommendations for all four major diet approaches — keto, low-carb, moderate (DGA standard), and high-carb/athletic — so you can compare options side by side. It also outputs fibre requirements and added sugar limits based on current guidelines.

Why Carbohydrates Matter: The Body's Primary Fuel Source

Carbohydrates are the body's preferred energy source, particularly for the brain, which requires approximately 120g of glucose per day and cannot efficiently use fat or protein as a substitute in normal metabolic states. Muscles also prefer glucose for high-intensity exercise, making carbohydrates especially important for athletes and anyone doing strength training or interval exercise. When dietary carbohydrates are sufficient, the body stores glucose as glycogen in muscles (~400g) and the liver (~100g), providing an energy reserve for exercise and fasting periods.

Complex carbohydrates (whole grains, legumes, vegetables) digest slowly, providing steady glucose release and sustained energy. Simple carbohydrates (added sugars, refined flour) digest rapidly, producing sharp blood glucose spikes followed by crashes. The Glycemic Index (GI) and Glycemic Load (GL) quantify this effect. The quality of carbohydrates matters as much as the quantity — 200g of carbohydrates from brown rice, oats, and vegetables has very different metabolic effects from 200g from white bread and sugar, even though the gram count is identical.

Low-Carb and Ketogenic Diets: When They Work and When They Don't

Low-carb diets (typically 20–30% of calories from carbs, or 100–150g/day) and ketogenic diets (under 10% carbs, or 20–50g/day) have strong evidence for short-term weight loss and blood sugar control in type 2 diabetes and pre-diabetes. By restricting carbohydrates, these diets shift the body toward fat oxidation (fat burning) and, in the case of keto, toward ketosis — a metabolic state where the liver produces ketone bodies from fat as an alternative fuel for the brain.

However, low-carb and keto diets are not universally superior. Endurance athletes (marathon runners, cyclists, triathletes) see performance declines on very low-carb diets because glycolysis (the glucose-burning pathway) is simply more efficient than fat oxidation for sustained high-intensity efforts. People with liver or pancreatic disease should consult a doctor before attempting ketogenic eating. Long-term ketogenic diets may also affect bone density and lipid profiles. For most healthy adults without specific medical conditions, moderate carbohydrate intake within dietary guidelines is appropriate and sustainable.

Fibre: The Most Overlooked Carbohydrate

Dietary fibre is a type of carbohydrate that the body cannot digest — it passes through the small intestine intact and is fermented by bacteria in the large intestine. The Dietary Guidelines for Americans recommend 14g of fibre per 1,000 kcal consumed, equating to 25g/day for adult women and 38g/day for adult men. Most people consume far less: the average American eats only about 15g/day. Fibre from whole foods (not supplements) is associated with reduced risk of cardiovascular disease, type 2 diabetes, colon cancer, and obesity.

Fibre is also key to understanding net carbs — the concept used in low-carb and keto tracking. Net carbs = total carbs − fibre. Fibre subtracts from total carbs because it does not raise blood glucose or require insulin secretion. This is why high-fibre foods (black beans, lentils, artichokes) have a much lower blood glucose impact than their total carb count suggests. On a 50g total carb keto budget, a single avocado (12g total carbs, 10g fibre = 2g net carbs) barely registers.