Carb Calculator
Enter your details below to find out exactly how many grams of carbohydrates you need each day. The calculator uses your Basal Metabolic Rate (Mifflin-St Jeor formula), your activity level, and your chosen carb percentage to give you a personalised daily target. Switch between metric and imperial units, pick a diet preset (keto, low-carb, balanced, or high-carb), and see how carbs fit alongside protein and fat in your full macro breakdown.
How your daily carb intake is calculated
This calculator follows a three-step process. First, it estimates your Basal Metabolic Rate (BMR), the calories your body burns at complete rest, using the Mifflin-St Jeor equation: 10 x weight (kg) + 6.25 x height (cm) - 5 x age + 5 for men, or the same formula minus 161 for women. Second, your BMR is multiplied by an activity factor (1.2 for sedentary up to 1.9 for very active) to give your Total Daily Energy Expenditure (TDEE). Third, your chosen carb percentage is applied to that calorie total, and the resulting calorie figure is divided by 4 (since carbohydrates provide 4 kcal per gram) to give your daily carb target in grams. If you selected a weight-loss or weight-gain goal, 500 kcal is subtracted or added before applying the percentage, targeting roughly 0.5 kg of fat change per week.
What are carbohydrates and why do they matter?
Carbohydrates are organic molecules made of carbon, hydrogen, and oxygen. They are classified broadly into simple carbohydrates (sugars such as glucose, fructose, and sucrose) and complex carbohydrates (starches and fibre found in whole grains, legumes, and vegetables). Once digested, most carbohydrates are converted to glucose, the primary fuel for the brain and muscles. The Institute of Medicine sets the minimum recommended dietary allowance at 130 g per day for adults, representing the minimum amount of glucose the brain needs. The USDA Dietary Guidelines recommend that carbohydrates make up 45-65% of total daily calories for most healthy adults. Fibre, a type of carbohydrate the body cannot fully digest, should account for at least 25-38 g per day for adults; it slows digestion, stabilises blood sugar, and feeds beneficial gut bacteria.
Choosing the right carb percentage for your goals
There is no single correct carb percentage: the right amount depends on your health goals, metabolic health, activity type, and food preferences. For general health and most active lifestyles, 45-65% of calories from carbohydrates aligns with major guidelines and makes it easy to meet fibre and micronutrient targets. Athletes doing prolonged endurance work may benefit from 60-70% to keep glycogen stores full. People managing blood sugar, insulin resistance, or wanting rapid initial weight loss often do better at 25-40%. Ketogenic diets (below 10%, typically under 50 g per day) shift metabolism toward fat-burning but require significant adjustment and are best undertaken with medical oversight. Whatever percentage you choose, quality matters: whole grains, legumes, fruit, and non-starchy vegetables deliver fibre, vitamins, and minerals alongside energy, while refined sugars and white flour products offer calories with little else.
Carbs, protein, and fat: balancing all three macros
Carbohydrates do not exist in isolation; any change to carb intake affects how much room is left for protein and fat. This calculator holds protein at a fixed 20% of calories as a sensible minimum for muscle maintenance, then allocates the remaining calories to fat. In practice, protein needs vary by body weight and activity: strength athletes commonly target 1.6-2.2 g per kg of body weight per day, which can push protein above 20%. If you have a specific protein target, adjust your carb and fat percentages to fit within your total calorie allowance. The most important principle is that total calories determine weight change; the macro split shapes body composition, energy, and how satisfied you feel on those calories.
Carbohydrate intake by diet type
| Diet type | Carbs (% of calories) | Typical daily range | Notes |
|---|---|---|---|
| Ketogenic | < 10% | 20-50 g | Induces ketosis; very restrictive |
| Very low-carb | 10-25% | 50-130 g | Below IOM minimum; medical supervision advised |
| Low-carb | 25-40% | 130-200 g | Popular for weight loss and blood sugar control |
| Moderate | 40-50% | 200-250 g | Suits many active individuals |
| Balanced (USDA) | 45-65% | 225-325 g | USDA Dietary Guidelines recommendation |
| High-carb | > 65% | > 325 g | Suited to endurance athletes |
Typical carb percentage ranges and minimum daily intake thresholds from major nutrition guidelines. Actual needs vary by body size, activity, and health status.
Frequently asked questions
How many grams of carbs should I eat per day?
It depends on your body size, activity level, and goals. For a 75 kg moderately active adult, a balanced 55% carb diet typically works out to around 250-300 g per day. The IOM minimum for adults is 130 g/day to fuel the brain. For weight loss or low-carb diets, intakes of 50-150 g/day are common. For endurance athletes, 300 g or more per day is often appropriate.
What is the Mifflin-St Jeor formula?
It is the most widely validated equation for estimating resting calorie needs in adults. For men: BMR = 10 x weight (kg) + 6.25 x height (cm) - 5 x age + 5. For women: BMR = 10 x weight (kg) + 6.25 x height (cm) - 5 x age - 161. The result is multiplied by an activity factor (1.2 to 1.9) to get your Total Daily Energy Expenditure (TDEE).
How many calories are in 1 gram of carbohydrates?
Exactly 4 kcal per gram, the same as protein. Fat provides 9 kcal per gram and alcohol 7 kcal per gram. To convert a carb calorie target into grams, divide by 4; to go the other way, multiply grams by 4.
What is the minimum safe carb intake?
The Institute of Medicine sets the Recommended Dietary Allowance (RDA) for carbohydrates at 130 g per day for adults, based on the minimum amount of glucose needed to fuel the brain. Very-low-carb and ketogenic diets go below this threshold intentionally; the brain adapts by using ketone bodies as an alternative fuel, but this adaptation takes several weeks and may cause fatigue, headaches, and irritability in the interim.
Should I eat more carbs if I exercise a lot?
Yes, especially for endurance or high-volume training. Muscles store carbohydrates as glycogen, and high-intensity exercise depletes glycogen rapidly. Research consistently shows that higher carb intakes support better performance, faster recovery, and preserved muscle mass in athletes doing prolonged aerobic or intermittent high-intensity work. Strength and power athletes have somewhat lower carb needs but still benefit from carbs around training sessions.
What counts as a carbohydrate?
All sugars (glucose, fructose, sucrose, lactose), starches (found in grains, legumes, and root vegetables), and dietary fibre are carbohydrates. Fibre is counted in total carbohydrate grams on food labels, but because it is not fully digested it contributes fewer usable calories. Some people track "net carbs" (total carbs minus fibre) when following low-carb diets.