Your daily carbs,
calculated precisely.

Field guide

How to calculate your daily carbohydrate needs.

Carbohydrates are the body's primary fuel source for high-intensity exercise and the preferred energy substrate for the brain. Yet daily carb needs vary enormously, from under 50 grams on a ketogenic diet to 500+ grams for competitive endurance athletes. The number that's right for you depends on four factors: your resting metabolic rate, your activity level, your body composition goal, and your preferred dietary framework.

This calculator personalises your carbohydrate target by first establishing your total energy expenditure, then calculating the carb fraction that matches your chosen approach, all in real time.

Step 1: Basal Metabolic Rate (Mifflin-St Jeor)

The calculator begins with the Mifflin-St Jeor equation (1990), the most validated BMR formula for the general adult population:

This gives the calories needed at complete rest. It was selected over the original Harris-Benedict (1919) formula because Mifflin and St Jeor validated theirs against modern indirect calorimetry data, making it consistently more accurate for adults across a broad BMI range.

Step 2: Total Daily Energy Expenditure (TDEE)

BMR is multiplied by an activity factor to produce your Total Daily Energy Expenditure:

Step 3: Goal adjustment

A small calorie modifier is applied based on the weight goal: a 20% deficit for weight loss (roughly 1 lb/0.45 kg per week), maintenance at TDEE, or a 10% surplus for lean muscle gain. Your carb target is then computed from this adjusted calorie figure.

The six carb approaches

Carbohydrate intake is expressed as a percentage of total daily calories. This calculator covers six evidence-based and widely-used frameworks:

Keto (≈5% of calories)

The ketogenic diet restricts carbs to roughly 20–50 g/day, forcing the body to produce ketone bodies from fat as the primary energy substrate. Rigorous research supports keto for epilepsy management and shows modest advantages for short-term weight loss compared to low-fat diets. It requires careful electrolyte management and may impair peak anaerobic performance during the adaptation period.

Low-carb (≈20% of calories)

Low-carb diets reduce carbs to roughly 50–150 g/daywithout inducing full ketosis. Meta-analyses show they produce similar weight loss to low-fat diets over 12 months. Many people find appetite suppression easier to sustain on low-carb, making adherence the key practical advantage.

Standard (45%, USDA RDA)

The U.S. Dietary Guidelines recommend 45–65% of calories from carbohydrates. At 45%, this is the lower boundary of general health recommendations, suitable for sedentary or lightly active individuals and consistent with major epidemiological findings linking moderate carb intake to metabolic health.

Balanced (50%)

A 50% carbohydrate allocation is the most common target in general fitness programming. It provides sufficient glycogen for moderate exercise (3–5 sessions/week) while leaving room for adequate protein and fat. It aligns with the Mediterranean dietary pattern, which consistently ranks among the most studied diets for cardiovascular health and longevity.

Athletic (60%)

Endurance athletes performing 10+ hours/week of training typically need 6–10 g of carbohydrate per kilogram of body weight per day, often 55–65% of total calories. At this level, glycogen stores are maximally replenished, supporting repeated high-intensity sessions without progressive glycogen depletion ("chronic fatigue" in athletes). This framework underpins carbohydrate periodisation strategies used by professional cyclists, marathon runners, and triathletes.

Carbohydrate needs by activity level (g/kg body weight)

The American College of Sports Medicine (ACSM) and the International Society of Sports Nutrition (ISSN) recommend carbohydrate intake in grams per kilogram of body weight, a scale that's independent of total calorie targets:

Carb timing: before and after exercise

Pre-workout (1–4 hours before): Consuming carbohydrates before training tops off muscle glycogen stores and maintains blood glucose during the session. The ACSM recommends 1–4 g/kg in the 1–4 hours before exercise. A 70 kg athlete at moderate intensity might target 70–140 g (a bowl of oatmeal and a banana, for example). For sessions under 60 minutes, a smaller snack of 30–60 g is typically sufficient.

Post-workout (within 2 hours): Glycogen resynthesis is fastest in the first 30–60 minutes after exercise. ISSN guidelines recommend 1–1.2 g/kg immediately after training, ideally paired with 20–40 g of protein to accelerate muscle protein synthesis. For a 70 kg athlete: 70–84 g carbs post-workout is a practical target.

Net carbs vs. total carbs

Total carbs includes all carbohydrate: sugars, starches, and dietary fiber. Net carbs = total carbs − dietary fiber. Fiber passes through the digestive tract largely undigested, contributing minimal calories and causing little glycemic response. Keto and low-carb dieters typically track net carbs; general and athletic dieters typically track total carbs.

The FDA recommends 25–38 g of fiber per day (women/men respectively). High-fiber carb sources (legumes, oats, vegetables, whole grains) simultaneously satisfy carb targets and fiber recommendations, making them nutritionally efficient choices across all six frameworks.

Glycemic index and blood sugar

The Glycemic Index (GI) ranks foods by how quickly they raise blood glucose. Low-GI foods (oats, sweet potatoes, lentils) produce a slower, more sustained glucose release. High-GI foods (white rice, sports drinks, candy) spike blood glucose rapidly.

For most people, GI is less important than total carbohydrate quantity. However, for individuals managing insulin sensitivity, type 2 diabetes, or reactive hypoglycemia, choosing lower-GI carb sources can meaningfully improve blood sugar control. Glycemic Load (GL): GI × grams / 100, which accounts for portion size and is a more practical real-world metric than GI alone.

Signs you may need to adjust carb intake

• Persistent fatigue during workouts: may signal glycogen depletion; increase carbs, particularly pre/post-workout.
• Brain fog or poor concentration: the brain uses ~120 g of glucose daily; insufficient carbs can impair cognitive performance on tasks requiring sustained attention.
• Difficulty maintaining weight despite large deficits, which may indicate metabolic adaptation; a temporary refeed day (higher-carb day) can restore leptin levels and reset the thyroid.
• Poor recovery between sessions: glycogen resynthesis takes 24–48 hours; inadequate carbs extend recovery time and increase overtraining risk.

Carb cycling

Carb cycling alternates high-carb days (training days) with low-carb days (rest or light days). The strategy attempts to preserve glycogen for hard sessions while promoting fat oxidation on easy days. It is popular with physique athletes and is supported by some evidence for body composition improvement, though it is more complex to implement than a fixed daily target.

A simple implementation: use this calculator to set your "training day" carb target (e.g., Balanced 50%), then reduce by 30–40% on rest days. Protein and fat intake remains constant across both day types to preserve lean mass.

Disclaimer

This calculator provides educational estimates based on validated formulas and sports-nutrition guidelines. Individual carbohydrate tolerance varies based on insulin sensitivity, gut microbiome, and training adaptation. For personalised dietary planning, especially if managing a health condition, consult a registered dietitian or sports nutritionist.