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How many calories to eat on 16/8 intermittent fasting?

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Reviewed by: Martín Rodríguez (política editorial ) · Last reviewed: 4 jun 2026

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16/8 intermittent fasting tells you when to eat — not how many calories or how to distribute them. Eating too much cancels the deficit; eating too little in 8 hours risks muscle loss. This calculator uses the Mifflin-St. Jeor equation (1990), endorsed by the American Academy of Nutrition and Dietetics (AND) as the most accurate formula for resting energy expenditure, to calculate your BMR, your real TDEE, and split your target calories across three balanced meals inside your eating window.

Last reviewed: June 3, 2026 Verified by Martín Rodríguez Source: Mifflin MD et al. — A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247, examine.com — 16:8 Intermittent Fasting: Human Evidence Summary, Tinsley GM, La Bounty PM — ISSN Position Stand: Meal frequency and timing in health and disease. J Int Soc Sports Nutr. 2015, Johns Hopkins Medicine — Intermittent Fasting: What Is It, and How Does It Work?, NIH National Institute on Aging — What Do We Know About Intermittent Fasting? 100% private

On 16/8 intermittent fasting you should eat the same total calories as without fasting — your TDEE for maintenance, or 15–25% less to lose weight. For a lightly active woman, 65 kg, 165 cm, 30 years old, that means roughly 1,601 kcal/day split across the 8-hour window as: Meal 1 (break-fast) 560 kcal (35%) → Main meal 640 kcal (40%) → Snack 401 kcal (25%). The Mifflin-St. Jeor equation calculates your personal target; this calculator does it instantly.

When to use this calculator

Planning a week of 16/8 meals without manual calculations, knowing exactly how many calories each meal should contain.
Adjusting your calorie target when switching goals — from a weight-loss deficit to maintenance or a muscle-building surplus.
Using the output as a science-backed starting point to review with a registered dietitian.
Checking whether a meal plan you found online is actually appropriate for your individual TDEE.

Example: female, 65 kg, 165 cm, 30 years old, lightly active, mild deficit

BMR (Mifflin-St. Jeor, female): 10×65 + 6.25×165 − 5×30 − 161 = 650 + 1,031 − 150 − 161 = 1,370 kcal/day
TDEE (activity ×1.375): 1,370 × 1.375 = 1,884 kcal/day
Mild deficit target (−15%): 1,884 × 0.85 = 1,601 kcal/day
8-hour window split: Meal 1 (35%) = 560 kcal | Main meal (40%) = 640 kcal | Snack (25%) = 401 kcal

Result: Target: 1,601 kcal/day · Meals: 560 / 640 / 401 kcal

How it works

2 min read

How many calories on 16/8 intermittent fasting?

The short answer: the same as without fasting. The 16/8 protocol controls when you eat, not how much. What changes is that you must distribute your full daily intake within 8 hours.

Quick-reference TDEE table by profile

Profile	Sedentary	Lightly active	Moderately active
Woman, 60 kg, 165 cm, 25 yrs	1,440 kcal	1,980 kcal	2,230 kcal
Woman, 70 kg, 165 cm, 35 yrs	1,530 kcal	2,100 kcal	2,370 kcal
Man, 75 kg, 175 cm, 25 yrs	1,850 kcal	2,540 kcal	2,870 kcal
Man, 85 kg, 180 cm, 35 yrs	1,940 kcal	2,670 kcal	3,010 kcal

Approximate values. Use the calculator above for your exact profile.

How It's Calculated

This calculator combines three standard steps used by registered dietitians:

#### 1. Basal Metabolic Rate (BMR) — Mifflin-St. Jeor Equation (1990)

BMR is the energy your body burns at complete rest (breathing, circulation, temperature regulation).

Men:   BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161

Published in the American Journal of Clinical Nutrition (1990) and officially recommended by the American Academy of Nutrition and Dietetics (AND) as the most accurate equation for estimating resting energy expenditure in healthy adults, with a typical error of ±10%.

#### 2. Total Daily Energy Expenditure (TDEE)

TDEE = BMR × Activity Factor

Level	Factor
Sedentary	1.2
Lightly active	1.375
Moderately active	1.55
Very active	1.725
Extra active	1.9

#### 3. Goal Adjustment and 16/8 Meal Distribution

Goal	Adjustment
Maintenance	TDEE × 1.0
Mild deficit	TDEE × 0.85 (−15%)
Moderate deficit	TDEE × 0.75 (−25%)
Surplus (muscle)	TDEE × 1.10 (+10%)

The target calories are then split across the 8-hour eating window:

Meal	Share	Rationale
Meal 1 (break-fast)	35%	Moderate protein + fibre breaks the fast and stabilises blood sugar
Main meal	40%	Largest meal, timed for highest insulin sensitivity
Snack / Meal 3	25%	Light, preferably lower in simple carbs

Macro reference (30/40/30 split)

For 16/8 IF, a balanced starting macro split is:

Protein: 30% of calories ÷ 4 kcal/g — priority to preserve muscle on a deficit

Carbohydrates: 40% of calories ÷ 4 kcal/g

Fat: 30% of calories ÷ 9 kcal/g

Note: These are population-level estimates. Individual response varies based on body composition, hormone levels, and training status. A registered dietitian can tailor these numbers to your specific physiology.

Disclaimer: Results are for informational purposes only and do not replace advice from a licensed healthcare provider. Do not use this calculator if you are pregnant, breastfeeding, have type 1 diabetes, kidney disease, or a history of eating disorders without first consulting your doctor.

Frequently asked questions

How many calories should I eat during my 8-hour window?

The same number you'd need without fasting — your TDEE for maintenance, or a 15–25% deficit for weight loss. The time restriction itself doesn't guarantee a calorie deficit; total energy intake still drives body composition. This calculator estimates that number for you using the Mifflin-St. Jeor equation.

What is 16/8 intermittent fasting?

It's a time-restricted eating (TRE) protocol: you fast for 16 consecutive hours and eat during an 8-hour window. It doesn't prescribe specific foods, only when you eat them. The 12 pm–8 pm window is common, but the window can be shifted to fit your schedule.

Why use Mifflin-St. Jeor instead of Harris-Benedict?

The Mifflin-St. Jeor equation (1990) was validated against indirect calorimetry in modern subjects and outperformed Harris-Benedict (1919) in accuracy. The American Academy of Nutrition and Dietetics reviewed multiple equations in 2005 and recommended Mifflin-St. Jeor as the most reliable for estimating resting metabolic rate, with a ±10% error in most adults.

Does 16/8 help with weight loss without counting calories?

Studies show that 16/8 can reduce spontaneous calorie intake by 10–15% on average, but it doesn't guarantee a deficit for everyone. People who compensate by eating denser or larger meals within the window may not lose weight. The most consistent results come from combining time restriction with awareness of total energy intake.

How much protein do I need on 16/8?

The International Society of Sports Nutrition (ISSN) recommends 1.6–2.2 g per kg of body weight per day for those who train and want to preserve or build muscle. At the higher end of a calorie deficit, aiming for 2.0–2.2 g/kg helps minimise muscle loss. Spread protein across your meals — at least 20–25 g per meal stimulates muscle protein synthesis (MPS).

Can I exercise while fasting on 16/8?

Yes. Training at the end of the fasting period (just before your first meal) can enhance fat oxidation and maximise post-exercise insulin sensitivity. If you train in the evening, schedule your main meal shortly after exercise to support muscle recovery. Both strategies are viable — choose the one that fits your schedule and feels sustainable.

Is 16/8 intermittent fasting safe?

For most healthy adults, 16/8 is considered safe and well-tolerated. It is not recommended without medical supervision for: pregnant or breastfeeding women, people with type 1 diabetes or insulin-dependent medications, those with a history of disordered eating, individuals under 18, and people with kidney or liver disease. Always consult your doctor before starting any fasting protocol.

Should I eat 2 or 3 meals inside the 8-hour window?

Research on time-restricted eating typically uses 2–3 meals. Three meals (35/40/25% split) maintains more stable blood glucose and distributes protein synthesis signals throughout the window. Two larger meals work for some people, especially those with smaller appetites or busy schedules. Experiment and track which pattern leaves you most satiated and energetic.

How long until I see results on 16/8?

Most people notice improved energy and mental clarity within 1–2 weeks as the body adapts to fat-burning during the fasting period. Body composition changes (fat loss, improved muscle definition) typically become visible within 4–6 weeks of consistent adherence. Sustainable weight loss is 0.5–1 kg per week; faster loss usually indicates muscle or water loss rather than fat.