Macro calculator: calories, protein, carbs, and fat with the formula shown

The exact method, step by step

Most macro calculators show a result and hide the route. Here is the whole route, using a 30-year-old, 5'10", 185 lb man who lifts three times a week and wants to maintain:

1. Resting energy (BMR). Mifflin-St Jeor: 10 × 83.9 kg + 6.25 × 177.8 cm − 5 × 30 + 5 = 1,805 kcal. The equation was derived from indirect calorimetry in 498 healthy adults and validated repeatedly since.
2. Estimated TDEE. Multiply by the activity factor. Lightly active is 1.375, so 1,805 × 1.375 ≈ 2,482 kcal. This is the least certain step in any calculator, which is why it should be replaced by measured data as soon as you have some.
3. Goal adjustment. Maintenance applies no change. Fat loss applies −20%, recomposition −10%, strength and bodybuilding +5%, lean bulk +10%. A 20% deficit on 2,482 kcal is 1,986 kcal, roughly the rate the contest-prep literature supports for preserving muscle.
4. Protein. Set by goal: 1.0 g/lb for fat loss and recomposition, 0.9 g/lb for lean bulk and bodybuilding, 0.8 g/lb for strength and maintenance. Cutting with a goal weight entered anchors protein to the goal weight instead of current weight.
5. Fat floor. 0.3 g per lb of current bodyweight, for hormonal support and food that is actually eatable day after day.
6. Carbohydrate. Whatever calories remain after protein (4 kcal/g) and fat (9 kcal/g) are funded, divided by 4 kcal/g. Carbs are the training fuel, not the leftover villain.

Every parameter, in one table

These are the shipped values from the Flexbound calculator (version iifym-v1). They live in versioned methodology data, so the app can tune them without changing the documented method:

Where every formula-based calculator is wrong

Two people with identical stats can differ by several hundred daily calories. Activity multipliers were never precise; people also systematically misjudge their own category, usually upward. The honest way to use this page: pick the number, eat near it consistently for two to three weeks while logging food and morning weight, then let the trend correct the formula. Energy-balance modeling shows that consistent intake logs plus a bodyweight trend recover your true expenditure far better than any equation. That correction loop is exactly whatFlexbound's adaptive TDEE automates, using only days you marked as completely logged.

Frequently asked questions

How accurate is a macro calculator?

A formula-based estimate is typically within about 10% of measured resting energy for most healthy adults, but individuals can sit further out, and activity multipliers add more uncertainty. Treat the output as a starting point, then adjust from two to three weeks of logged intake and bodyweight trend rather than trusting the formula indefinitely.

Which BMR equation does this calculator use?

Mifflin-St Jeor (1990): 10 × weight in kg + 6.25 × height in cm − 5 × age, then +5 for men or −161 for women. It remains the most consistently validated general-population resting-energy equation and is the same equation the Flexbound app ships.

Why is protein anchored to goal weight when cutting?

When you carry meaningful extra fat mass, anchoring protein to current bodyweight inflates the target without protecting any additional muscle. Anchoring to goal weight keeps the target tied to the lean mass you are protecting. If you have no target weight set, the calculator anchors to current weight.

Should I eat the same macros on rest days?

The targets here are daily averages built from a weekly energy budget. Most lifters adhere better with the same daily target than with cycling. If you prefer training-day and rest-day splits, keep the weekly total the same and hold protein steady every day.