About the Carb Calculator
Carbohydrate sits oddly among the macros, and using it well means holding two facts at once that sound contradictory.
There is no minimum requirement.
And it is the performance macro.
Both are true, and the tension between them is the whole subject. This carb calculator gives a target by training load, and then answers the question that turns out to be more useful: how much can you actually store?
How to Use the Carb Calculator
Enter your bodyweight and pick a training load.
Optionally add daily calories with your protein and fat figures, and carbohydrate becomes the remainder — which is usually how it should be treated.
Step-by-Step Example
70kg, moderate training.
3 to 5 g/kg × 70 kg = 210 to 350 g a day
840 to 1,400 caloriesAnd the storage side:
Muscle (40% of 70 kg × 15 g/kg): 420 g
Liver: 100 g
─────
Total glycogen: 520 g = 2,080 calories
After carb loading: 940 gNo Minimum Requirement — Really
This genuinely distinguishes carbohydrate from the other two macros, and it is not a technicality.
Protein supplies amino acids the body cannot synthesise. Fat supplies two essential fatty acids — linoleic and alpha-linolenic — that must come from food.
Carbohydrate supplies nothing the body cannot make. Through gluconeogenesis, glucose is manufactured from protein and from the glycerol backbone of fats. There is no essential carbohydrate.
The official minimum figures you will see, around 130g a day, exist to cover the brain's preference for glucose — roughly 120g a day of it — not a dietary necessity. That is why very low-carb diets are viable at all.
But No Minimum Is Not Optimal at Zero
The second fact, and it is equally real.
Anything above moderate intensity runs on muscle glycogen, and muscle glycogen comes from dietary carbohydrate. Fat oxidation cannot supply energy fast enough at high intensities; that is a rate limit, not a preference.
So endurance work can need 6 to 10 g per kilogram a day — 420 to 700g for a 70kg athlete, which is a very great deal of food. And it needs replacing daily, because it depletes daily.
What you give up on a low-carb diet is not health. It is the fuel for intensity. Low-intensity work feels normal; anything hard feels considerably harder.
The Ceiling
Here is the part that makes carb loading a number rather than an instruction.
Glycogen storage has a hard limit. Muscle holds roughly 15g per kilogram of muscle tissue, and the liver about 100g. Supercompensation — the loading protocol — roughly doubles the muscle portion and no further.
| 70kg person | Glycogen |
|---|---|
| Normal | 520 g |
| After loading | 940 g |
| After eating more than that | 940 g |
Carbohydrate eaten beyond the ceiling does not become extra stored fuel. It is used for that day's energy, or it is not, but the tank is full either way.
So "carb loading" has an end point. The calculator computes it for your body, which turns a vague instruction into a target you can actually hit and then stop.
Carbs as the Remainder
The sensible order of operations across all three macros:
- Protein — set by bodyweight, because it has a requirement tied to your
body.
- Fat — kept above its floor, because hormone production and vitamin
absorption depend on it.
- Carbohydrate — whatever is left.
That order is not arbitrary. It puts the macro with no minimum requirement last, where it has room to absorb whatever the other two leave, and it lets you adjust carbohydrate up or down according to how hard you are training without disturbing anything essential.
The calculator supports this directly: give it calories, protein and fat, and it reports the remainder rather than a generic target.
Fibre Is Carbohydrate That Does Not Behave Like It
Worth separating, because it sits inside the carbohydrate total and follows none of the rules above.
Fibre is carbohydrate the human gut cannot digest. It contributes little usable energy, it does not raise blood glucose meaningfully, and it does not become glycogen — so none of the fuelling arithmetic on this page applies to it. What it does instead is slow gastric emptying, feed gut bacteria, and add considerable volume to a meal for very few calories.
That last point is the practical one. A diet at the same carbohydrate total can feel entirely different depending on how much of it arrives as fibre, which is why two people hitting identical macros can report completely different hunger.
Some labelling conventions count fibre in the carbohydrate total and some subtract it, giving "net carbs". Neither is wrong; they are answering different questions. For fuelling, the net figure is the more useful one. For satiety and gut health, the fibre is the point.
Understanding Your Result
Carbohydrate a day is the target range, or the remainder where you supplied one.
The target range gives the per-kilogram figures and why.
What you can store is your glycogen ceiling, normal and loaded.
The minimum requirement states the no-essential-requirement point plainly.
Worth knowing flags a low remainder, an endurance target, or an overspend.
When Should You Use This Calculator?
Fuelling endurance training. The daily requirement is larger than most people expect.
Planning a carb load. It has a ceiling, and now you know yours.
Setting macros. Carbohydrate last, as the remainder.
Considering low carb. The no-minimum fact is why it works and the glycogen fact is what it costs.
Common Mistakes
Thinking carbohydrate is essential. It is the only macro that is not.
Concluding that means zero is fine. No requirement is not the same as no benefit.
Loading past the ceiling. Beyond about double your normal store it does nothing.
Cutting carbs and protein together in a deficit. Cut carbohydrate; hold protein.
Under-fuelling endurance work. Glycogen depletes daily and must be replaced daily.
Setting carbohydrate first. It is the macro with room to move, so it should go last.
These are general guidelines and individual requirements vary considerably with training, medication and medical conditions — anyone with diabetes in particular should take carbohydrate advice from a doctor. Nothing here is medical or dietary advice.