BMI, Macros, TDEE, Intermittent Fasting & Sleep Cycles — all in one place
When do you want to start eating? Noon is common for 16:8.
We factor in ~14 minutes to fall asleep.
MacroFast is a free, all-in-one health calculator designed to help you understand your body's nutritional needs. Whether you're trying to lose weight, build muscle, or simply eat more intentionally, knowing your numbers is the first step. This tool combines three evidence-based calculators into one simple interface — no sign-up required, no data stored.
Macronutrients — protein, carbohydrates, and fat — are the three main components of the food you eat. Each plays a distinct role in how your body functions, and getting the balance right can make a huge difference to your energy levels, body composition, and overall health.
Protein is essential for repairing and building muscle tissue, supporting immune function, and keeping you feeling full. For most people aiming to lose weight or build muscle, a target of 1.6–2.2g of protein per kg of bodyweight per day is a good starting point. Foods high in protein include chicken, eggs, Greek yogurt, lentils, and tofu.
Carbs are your body's primary energy source, particularly for brain function and high-intensity exercise. Rather than cutting them out entirely, focus on the quality: whole grains, fruits, vegetables, and legumes provide fibre and micronutrients alongside their energy. Refined sugars and ultra-processed carbs are the ones worth reducing.
Dietary fat is critical for hormone production, vitamin absorption (A, D, E, K), and brain health. Healthy fat sources include avocados, olive oil, nuts, seeds, and oily fish. The key is distinguishing unsaturated fats (beneficial) from trans fats (harmful).
Your Total Daily Energy Expenditure is the total number of calories your body burns in a day, accounting for your Basal Metabolic Rate (the calories needed just to stay alive) plus the energy used during physical activity. Eating below your TDEE creates a calorie deficit for weight loss; eating above it supports muscle gain.
Intermittent fasting (IF) is an eating pattern that cycles between periods of eating and fasting. Unlike traditional diets, it doesn't prescribe what you eat — only when. It has become one of the most popular approaches to weight management and metabolic health, backed by a growing body of research.
The most popular IF protocol: you fast for 16 hours and eat within an 8-hour window. Most people skip breakfast and eat between noon and 8pm, though you can shift the window to suit your lifestyle. It's widely considered the most sustainable IF approach for beginners.
A slightly more restrictive version, with an 18-hour fast and a 6-hour eating window. Many people find this a natural progression after a few weeks of 16:8, and it can accelerate weight loss results when combined with a moderate calorie deficit.
Originally popularised by Ori Hofmekler, the 20:4 approach involves a 20-hour fast with one main meal in a 4-hour window, typically in the evening. It suits people who naturally aren't hungry during the day and prefer one larger meal.
The most extreme mainstream IF protocol — eating all your daily calories in a single 1-hour window. OMAD can be very effective for weight loss but requires careful attention to nutrient density to ensure you're meeting your daily needs in one sitting. It's not recommended for beginners.
Always consult a healthcare professional before starting any fasting protocol, particularly if you have a history of disordered eating, diabetes, or other metabolic conditions.
The calculator uses the Mifflin–St Jeor equation, which is considered the most accurate formula for estimating resting metabolic rate in the general population. That said, all TDEE calculators are estimates — individual metabolism varies based on genetics, muscle mass, hormones, and other factors. Use the result as a starting point and adjust based on real-world results after 2–3 weeks.
The activity multiplier in this calculator already accounts for your exercise level, so your TDEE result includes those calories. You don't need to add them back separately — just select the activity level that best describes your typical week.
For most healthy adults, intermittent fasting is safe and well-tolerated. It is not recommended for pregnant or breastfeeding women, people under 18, those with a history of eating disorders, or anyone with conditions that require regular food intake. When in doubt, speak to your GP or a registered dietitian.
For most adults, a BMI between 18.5 and 24.9 is considered healthy. A BMI below 18.5 is classified as underweight, 25–29.9 as overweight, and 30 or above as obese. Note that BMI doesn't account for muscle mass — a very muscular person may have a high BMI despite being in excellent health.
The default 30/40/30 protein/carbs/fat split is a solid general-purpose starting point. Athletes or those doing heavy resistance training may benefit from higher protein (35–40%). Those following a low-carb or ketogenic approach would shift carbs much lower. Track your energy levels and performance for a few weeks and adjust from there.