Nutrition Needs Calculator Ireland — Energy, Protein & Macros

What this calculator is — and is not

This tool combines several related nutrition calculations on one page so you do not need separate BMR, TDEE, protein and macro calculators.

It is designed for generally healthy adults as an educational planning tool. It is not intended for pregnancy, breastfeeding, under-18s, people with an eating disorder, or people who need medical nutrition therapy. In those situations, energy and nutrient needs should be assessed appropriately by a clinician or dietitian.

Basic and Advanced modes

Basic answers the most common questions with the fewest assumptions: predicted resting energy, activity-adjusted maintenance energy and the general adult protein reference based on body weight. It deliberately avoids turning an estimate into a diet prescription.

Advanced adds the optional 10% higher/lower energy scenario, the resistance-training protein evidence point and an illustrative macro split. The added values make the arithmetic more useful for scenario planning, but they do not make the underlying estimate more clinically precise.

Resting energy: Mifflin–St Jeor

The resting-energy estimate uses the Mifflin–St Jeor equation, published in the American Journal of Clinical Nutrition in 1990. A systematic review comparing commonly used equations found Mifflin–St Jeor more likely than the alternatives assessed to estimate measured resting metabolic rate within 10% in non-obese and obese adults, while also emphasising meaningful individual errors.

That uncertainty matters. A calculated value such as 1,650 kcal/day should be read as an estimate, not as a measurement of your metabolism. Indirect calorimetry is the reference method when an accurate clinical measurement is needed.

From resting energy to maintenance energy

Total energy needs depend heavily on movement and activity. EFSA describes Physical Activity Level (PAL) as total daily energy use relative to resting energy and uses PAL values such as 1.4, 1.6, 1.8 and 2.0 to illustrate low-active through very-active adult lifestyles.

Compound multiplies the resting-energy estimate by the PAL you select. The weakest part of this calculation may be the activity selection itself: two people who both choose “moderately active” can have quite different true energy expenditure.

Why the ±10% scenarios are labelled illustrative

The 10% lower and higher options are mathematical scenarios, not weight-loss or weight-gain prescriptions. Appropriate energy intake can depend on health, training, body composition, medications, pregnancy status, previous dieting and other factors this calculator does not know.

Protein: general health versus resistance training

EFSA’s adult Population Reference Intake for protein is 0.83 g per kg of body weight per day. This is intended to cover the needs of the large majority of generally healthy adults consuming a mixed European diet.

For people doing resistance training, a 2018 systematic review, meta-analysis and meta-regression found that increases in fat-free mass with protein supplementation during resistance training plateaued at around 1.62 g/kg/day, with the confidence interval extending higher. Compound therefore uses 1.6 g/kg/day as an evidence point in the resistance-training option. It should not be interpreted as a minimum requirement for every gym user or proof that more protein is always better.

Does protein timing matter?

Total daily protein intake appears more important than treating a tiny post-workout window as mandatory. A 2025 meta-analysis directly comparing protein consumed before versus after exercise found no important difference in exercise-induced changes in lean body mass. A protein-containing meal around training is sensible, but the calculator does not pretend minute-by-minute timing can be reduced to one superior rule.

The macro illustration

Protein contributes approximately 4 kcal per gram. For the remaining macro illustration, Compound shows total fat at 30% of the selected energy figure, consistent with WHO guidance that adults limit total fat intake to 30% of total energy or less for prevention of unhealthy weight gain. Carbohydrate is then the mathematical remainder after protein and fat.

This is not a claim that every person should eat exactly 30% fat or that macro percentages determine diet quality. WHO emphasises quality as well as quantity: carbohydrate should come primarily from whole grains, vegetables, fruits and pulses; adults should consume at least 25 g/day of naturally occurring dietary fibre and at least 400 g/day of fruit and vegetables.

Use the result as a range of questions, not a precise prescription

Useful follow-up questions include:

• Does your actual body weight remain broadly stable around the estimated maintenance intake over several weeks?
• Is your chosen activity level realistic?
• Are you meeting protein needs through a varied diet?
• Are fibre, fruit, vegetables and food quality getting lost behind the macro numbers?
• Are you using the tool in a situation where professional nutrition advice would be safer?

The more precise the number looks, the easier it is to forget the uncertainty behind it. The purpose of the calculator is to make the assumptions visible.

Worked example

For a 30-year-old man weighing 80 kg and measuring 180 cm, the Mifflin–St Jeor equation estimates resting energy at roughly:

10 × 80 + 6.25 × 180 − 5 × 30 + 5 = 1,780 kcal/day.

If an activity factor of 1.6 is selected, the maintenance illustration becomes about 2,848 kcal/day.

If the resistance-training protein context is selected, 1.6 g/kg gives about 128 g protein/day. The calculator then allocates the remaining modelled energy to its fat and carbohydrate illustration.

Those figures are useful starting points, but they are still predictions. Two people with the same age, height and weight can have different measured energy expenditure.

Method and limitations

Resting energy is predicted with the Mifflin–St Jeor equation. Maintenance energy multiplies that result by the selected physical-activity factor. The optional ±10% energy scenarios are simple illustrations, not prescribed calorie deficits or surpluses.

Protein is set to the selected evidence context, fat is modelled at 30% of scenario energy and carbohydrate receives the remaining energy. The tool does not account for pregnancy, lactation, clinical disease, eating-disorder history, medication effects or measured metabolic data.

Frequently asked questions

Is this a weight-loss prescription?

No. The energy scenarios are planning illustrations and are not a clinical prescription. Weight management can be affected by health conditions, medications, pregnancy, eating-disorder history and many other factors.

Why use Mifflin–St Jeor?

It is a widely used predictive equation for resting energy expenditure in adults and has performed reasonably well in validation research, but every predictive equation has individual error.

Why does the resistance-training option use 1.6 g/kg?

A large 2018 meta-analysis by Morton and colleagues found that gains in fat-free mass from protein supplementation during resistance training appeared to plateau around 1.6 g/kg/day on average, while individual needs and confidence intervals vary.

Is more protein always better?

No. Once protein needs are met, additional protein does not automatically produce additional muscle or health benefit. Overall diet quality, total energy, training and medical context still matter.

Are the carbohydrate and fat numbers targets?

They are a transparent macro illustration after the protein assumption, not personalised dietary prescriptions.

Related Compound tools

Use the BMI Calculator for another population-level screening measure and read the nutrition guide alongside the calculator rather than treating one energy estimate as a precise daily requirement.