How to Set Up Your Nutrition Numbers
Calories, protein, macros and water in the order they depend on each other — and four widely-quoted figures that turn out to be minimums, not targets.
The tools in this guide
All free, no signup. Each one has a printable sheet too.
- Protein Intake CalculatorThe 0.8 g/kg RDA is a minimum to avoid deficiency, not a target. If you train, the published range is roughly double it.
- Macro Split CalculatorPercentages into grams - and a check that your three add to 100, which is where most macro plans quietly fail.
- Calorie Deficit Timeline CalculatorHow long a given deficit takes - built on the 3,500-calorie rule, which researchers have shown overestimates real weight loss. The tool says so.
- TDEE CalculatorWhat your body burns in a day, using the Mifflin-St Jeor equation - split into the part that is just staying alive and the part your activity adds.
- Daily Water Intake CalculatorThe 8x8 rule is 64 oz. The actual reference figure is 125 oz for men and 91 for women - and unlike 8x8, it counts food and every other drink.
- Daily Sodium Intake CalculatorSodium and salt are not the same number - 5 g of salt is 2,000 mg of sodium. Confusing them is a two-and-a-half-fold error.
- Daily Fibre Intake CalculatorThe 25 g and 38 g figures are not about being a woman or a man - they are 14 g per 1,000 calories at two assumed appetites.
Nutrition numbers only work in one order, because each one is a share of the one before it. Macros are a split of calories; calories come from your expenditure. Set them the other way round and the percentages describe nothing.
None of this is medical advice. These are general planning tools, and anything involving a medical condition, pregnancy or medication belongs with a clinician or a registered dietitian.
1. Start with what you burn
The TDEE Calculator uses the Mifflin–St Jeor equation and splits the answer into the part that is just staying alive and the part your activity adds.
This is the base number and everything else is a fraction of it. The activity multiplier is where the error lives — people consistently overestimate it. If your results are not matching over several weeks, revisit that setting before you doubt the equation.
2. Then the deficit, honestly
The Calorie Deficit Timeline Calculator is built on the 3,500-calories-per-pound rule, which researchers have shown overestimates real weight loss — and the tool says so.
The body adapts; the rule assumes it does not. Treat the output as the fastest plausible case rather than a schedule, and expect reality to run behind it. A plan built on the optimistic figure that then "fails" at week six was never failing.
3. Protein: the RDA is a floor
The Protein Intake Calculator clears up the most misused number in nutrition: the 0.8 g/kg RDA is a minimum to avoid deficiency, not a target. If you train, the published range is roughly double it.
Those are two different kinds of number. One is the point below which you develop a problem; the other is what supports what you are trying to do. Quoting the RDA at someone who lifts is answering a question they did not ask.
4. Macros: check they add to 100
The Macro Split Calculator turns percentages into grams, and checks your three add to 100 — which is where most macro plans quietly fail.
That sounds trivial and is not. Plans get adjusted one macro at a time — more protein this week, fewer carbs next — and after a few edits the split adds to 94 or 108 and every gram figure is wrong. It fails silently because each individual number still looks reasonable.
5. Water: the 8×8 rule is not the reference figure
The Daily Water Intake Calculator carries a genuinely useful correction. The 8×8 rule is 64 oz. The actual reference figure is 125 oz for men and 91 for women — considerably more.
But the second half matters as much: unlike 8×8, the reference figure counts food and every other drink. So it is not a demand for twice as many glasses of water. Most people get a substantial share from food, tea, coffee and everything else, and the reference total already assumes that.
Two different numbers measuring two different things, which is exactly why they seem to contradict.
The short version
- TDEE first — check the activity multiplier before anything else.
- Deficit timelines are the optimistic case, by construction.
- 0.8 g/kg is a floor. Training roughly doubles the published range.
- Make your macro percentages add to 100 after every edit.
- 125 oz / 91 oz is a total including food, not glasses of water.
Each tool ships with a printable that carries its own assumptions, so the caveats travel with the numbers instead of being lost the moment they go on the fridge.
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