As of 13 August 2026, AI can only partly calculate your macros.
Most people should hand this to a purpose-built tool.
Can you do it?
5 minutesto a draft.
30 minutesto something you’d act on.
Cost, all in£0
Skill neededchat-fluent
Who has to check ityou
What the alternative costsAn alternative is MacroFactor, an AI nutrition coaching app that adjusts targets from your logged data.
If this goes wrong: you follow an unsuitable calorie or macro target for weeks because the calculation looked precise.
What to actually do
Use a tool built for this
The route this page recommends
Do it yourself
Second choiceA chat interface, chat-fluent skill, and roughly 30 minutes until you can act on the result.
How to actually do it
- Gather your age, height, weight, the sex used for the chosen formula, usual activity, training, goal and any dietary limits.
- Open a chatbot and paste the prompt, replacing each bracketed slot with your information or writing that you prefer not to share.
- Ask the chatbot to recalculate if it makes an assumption about your activity, goal, units or desired rate of weight change that is not accurate.
- Check that the displayed protein, carbohydrate and fat grams convert to the stated calories using 4 calories per gram for protein and carbohydrate and 9 calories per gram for fat.
- Compare the assumptions and target range with guidance from a GP or registered dietitian if you are pregnant, breastfeeding, under 18, have a health condition, take relevant medicines or have a history of an eating disorder.
- Use the final range as a planning estimate, then track your food and weight over time and adjust only with appropriate professional support if the result causes problems.
Prompt
Calculate estimated daily calorie and macronutrient targets for me using the information below. Use metric units unless I specify otherwise. Age: [age] Sex used for the formula: [sex] Height: [height] Weight: [weight] Typical activity: [sedentary, lightly active, moderately active, very active, or a description of my week] Goal: [maintain weight, lose weight, or gain weight] Desired rate of change, if any: [details or leave blank] Training: [type, frequency and duration] Dietary pattern or limits: [details] Relevant health conditions, pregnancy or breastfeeding, history of an eating disorder, and medicines that may affect appetite or weight: [details or say prefer not to share] Show each step of the calculation, identify every assumption, and give a sensible range rather than false precision. State which formula or method you used and explain how the activity and goal adjustments affect the result. Give daily protein, carbohydrate and fat targets in grams, make the percentages add up, and show the calorie contribution from each macro. Do not diagnose me, prescribe treatment, or present this as medical advice. If my information suggests that a general macro target may be unsafe, say that clearly and tell me to speak to a GP or registered dietitian instead. If I mention urgent or worrying symptoms, tell me to contact NHS 111 or use 111.nhs.uk. End with the exact details I should confirm before using the estimate.
Open it prefilled in ChatGPT or Claude, or copy it into Gemini, which takes no prefill link.
Hand it to a person
The distant thirdA person who owns the outcome does this end to end, worth it when the failure is dear.
What it gets wrong
- AI cannot tell from arithmetic alone whether the target is safe for your medical history, medicines, pregnancy, breastfeeding or eating-disorder history.
- AI cannot measure your actual energy expenditure or confirm that your description of activity is accurate.
- AI cannot replace a registered dietitian or GP when weight change is connected to illness, treatment or worrying symptoms.
- AI gives a neat number even when the underlying estimate is uncertain, so precision can be mistaken for accuracy.
What caps this at PARTLY: judgement under ambiguity, stakes of error and context depth.
How we scored this
Five axes, each scored nought to two by hand: ten means AI carries the task cleanly, and the thresholds that turn a total into YES, PARTLY or NO are published in the methodology. Each axis name links to its definition.
| Axis | Score (0–2) |
|---|---|
| Output | 2 |
| Inputs | 1 |
| Verification | 1 |
| Liability | 1 |
| Effort delta | 2 |
| Total | 7 / 10 |
The methodology and its thresholds are published in full.
FAQ
- Can ChatGPT calculate my macros?
- Yes, it can produce an estimated calorie, protein, carbohydrate and fat target from your details. It cannot confirm that the target is suitable for your health, so check the assumptions and seek advice from a GP or registered dietitian when your circumstances are medically complicated.
- What information do I need to calculate my macros?
- Give your age, height, weight, the sex used for the formula, usual activity and goal. Include training, dietary limits, pregnancy or breastfeeding, relevant health conditions, medicines and any eating-disorder history because these can change whether a general estimate is appropriate.
- Are AI macro calculations accurate?
- They can be arithmetically consistent but they are estimates, because activity levels, food intake and energy needs are not measured precisely by a chat. Check the units, formula, assumptions and macro calorie totals rather than treating the result as an exact prescription.
- Is it safe to use AI to calculate macros?
- It is reasonable for general meal-planning estimates when you are well and provide accurate information, but it is not professional advice. Do not rely on it for a medical nutrition plan, and contact NHS 111 or use 111.nhs.uk for urgent or worrying symptoms.
Nearby answers
Assessed by gpt-5.6-luna (gpt-5.6-luna) on 2026-08-13, second-checked by an independent model. Wrong somewhere? Email [email protected] and it gets re-checked.
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