Carbohydrate Calculator
How many grams of carbs should you eat a day? Enter your age, sex, size, and activity level: the calculator estimates your maintenance calories with the Mifflin-St Jeor equation, then converts the official 45–65% guideline range into grams — at maintenance and at common weight-loss calorie targets.
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Learn moreHow your carb number is built
Carbohydrate needs aren’t fixed — they scale with how much energy you burn. So the calculator first estimates your resting metabolism from age, sex, height, and weight, multiplies by an activity factor to get total daily energy (TDEE), then applies the share of calories you want from carbs. Since carbohydrate provides 4 calories per gram, grams = calories × share ÷ 4. The 45–65% band is the Acceptable Macronutrient Distribution Range used by the Dietary Guidelines for Americans; endurance athletes often sit at the top of it, low-carb dieters below it.
How it’s calculated
BMR (Mifflin-St Jeor) = 10×kg + 6.25×cm − 5×age + 5 (men) or −161 (women). TDEE = BMR × activity factor (1.2–1.9). Carb grams = TDEE × carb% ÷ 4 kcal/g. The deficit table repeats the math at −250, −500, and −1,000 kcal/day (≈0.5, 1, and 2 lb/week). Guideline band: carbohydrate AMDR 45–65% of calories, RDA 130 g/day (Dietary Guidelines for Americans 2020–2025 / Institute of Medicine).
Educational estimates, not medical or dietetic advice. Energy equations carry ±10% error for individuals, and needs differ with diabetes, pregnancy, and medical diets — confirm targets with a clinician or registered dietitian.
Carbs at maintenance and in a deficit
Grams per day at 45%, 55%, and 65% of each calorie target; 4 kcal per gram.
Worked example
A 30-year-old man, 5′10″ and 165 lb, exercising 4–5 times a week: BMR ≈ 1,715 kcal, TDEE ≈ 2,512 kcal. His guideline carb range is 283–408 g/day (45–65%), and at a 50% share he’d aim for about 314 g. Cutting 500 kcal/day drops the 50% target to about 252 g.
Common mistakes
- Counting net carbs against a total-carb target — pick one convention and stick to it.
- Forgetting liquid carbs; juices and sodas can add 50–100 g/day without any fullness.
- Copying an athlete’s 65% plan while sedentary — share of calories only makes sense relative to your burn.
- Slashing carbs below 130 g while training hard and wondering why sessions feel flat.
Where it is used
- Building a daily macro plan for weight loss, maintenance, or muscle gain.
- Fueling endurance training weeks where carb needs climb.
- Setting grocery and meal-prep targets from a calorie budget.
- Comparing your current intake to the official guideline band.
Frequently asked questions
Is there a minimum amount of carbohydrate I need?
The Institute of Medicine sets the adult RDA at 130 grams per day, based on the glucose the brain typically uses. The body can adapt below that (ketogenic diets run 20–50 g), but 130 g is the standard reference minimum for mixed diets.
Why 45–65% of calories?
That is the Acceptable Macronutrient Distribution Range (AMDR) for carbohydrate used by the Dietary Guidelines for Americans 2020–2025. Within it, intakes are associated with adequate nutrients and lower chronic-disease risk; where you land inside the range is personal preference and training-dependent.
Do carbs make you gain weight?
Total calories drive weight change; carbs are 4 kcal per gram, the same as protein and less than fat’s 9. The catch is that refined carbs and sugary drinks are easy to overconsume. At the same calories, low-carb and low-fat diets produce similar average fat loss in trials.
How should the grams change when I’m cutting?
Keep protein high and take most of the deficit from carbs and fat. The deficit table applies your chosen carb percentage to reduced calorie targets — for example a 500 kcal/day deficit (about 1 lb per week) simply scales the gram range down proportionally.
How much fiber should I get?
The Dietary Guidelines reference is 14 g of fiber per 1,000 kcal — roughly 28 g on a 2,000-kcal diet. Whole grains, beans, fruit, and vegetables get you there; fiber counts inside your carb total, not on top of it.