Every weight, energy and body-composition goal ultimately comes down to one number: how much energy you actually burn in a day. This calorie calculator estimates that number in two clear layers. First it works out your Basal Metabolic Rate (BMR) — the calories you would burn if you simply rested all day. Then it multiplies that by your real activity level to get your Total Daily Energy Expenditure (TDEE), which is the amount you can eat while holding your weight steady. From there it offers a simple 500 kcal-per-day cut or bulk target so you know exactly where to aim.
The math underneath is the Mifflin-St Jeor equation, widely regarded as the most accurate general-purpose BMR formula for healthy adults. Adjust the sliders and every figure updates instantly, so you can stress-test how a different activity level, a weekend of exercise, or a small change in weight moves your target.
How to Use
- Enter your Age in complete years. BMR gently declines with age, so an up-to-date number matters more than you might expect.
- Choose your Sex — male or female — which applies the correct Mifflin-St Jeor constant.
- Type your Height in centimeters. If you usually work in inches, multiply by 2.54 first.
- Enter your Weight in kilograms. If you use pounds, divide by 2.20462.
- Pick your Activity Level honestly: sedentary (little intentional exercise, factor 1.2), light (light exercise 1–3 days a week, 1.375), moderate (moderate exercise 3–5 days a week, 1.55), active (hard exercise 6–7 days a week, 1.725), or very (very hard exercise or a physically demanding job, 1.9). Over-estimating activity is the single most common reason people stop losing weight despite "eating less."
- Set your Goal to maintain, lose, or gain. Lose applies a 500 kcal-per-day deficit; gain applies a 500 kcal-per-day surplus.
- Optionally add a Manual Adjustment in kcal/day to fine-tune the target after a couple of weeks of real-world tracking.
The result card shows your BMR, your maintenance calories (TDEE), your target daily calories, and an estimated weekly weight change. A 500 kcal daily deficit corresponds to roughly 0.45 kg (about one pound) of body fat per week, because one kilogram of stored fat is worth close to 7,700 kcal.
The Mifflin-St Jeor Formula
The equation the engine uses is:
- Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
- Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
Your TDEE is then BMR × the activity factor, and your target is TDEE plus or minus your chosen adjustment. For a 30-year-old man who is 175 cm tall and weighs 70 kg at a moderate activity level, BMR comes out to about 1,649 kcal, and multiplied by 1.55 gives a maintenance figure near 2,556 kcal per day. Choosing "lose" drops his target to about 2,056 kcal — a comfortable, sustainable deficit rather than an aggressive crash diet.
Why 500 kcal?
A 500 kcal daily deficit is the classic starting point because it balances speed with practicality. It is large enough to produce a visible, motivating change of roughly 0.45 kg per week (about 1 percent of body weight weekly for many adults), yet small enough that you are not ravenous and your strength and mood hold up. Going far below this — say a 1,000 kcal deficit — usually backfires: adherence collapses, muscle is lost alongside fat, and metabolism adapts. The same logic in reverse applies to gaining; a modest 500 kcal surplus builds mostly lean tissue rather than mostly fat.
To turn calories into meals, a common starting split is about 30 percent of calories from protein, 40 percent from carbohydrates and 30 percent from fats. On a 2,056 kcal target that is roughly 154 g of protein, 206 g of carbs and 69 g of fat per day.
Examples
Example 1 — A 30-year-old office worker. Male, age 30, 175 cm, 70 kg, sedentary (1.2), goal lose. BMR is about 1,649; maintenance is 1,649 × 1.2 ≈ 1,979 kcal. With a 500 kcal cut, his target is about 1,479 kcal/day, trending toward roughly 0.45 kg lost per week. Because his job is desk-bound, choosing "light" instead of "sedentary" would raise maintenance by nearly 300 kcal — a reminder that honest activity selection matters.
Example 2 — A moderately active woman. Female, age 25, 165 cm, 60 kg, moderate activity (1.55), goal maintain. BMR is about 1,345 kcal; maintenance is 1,345 × 1.55 ≈ 2,085 kcal/day. She eats to that number and holds her weight steady, spending roughly $40–$60 a week on groceries at typical macro ratios.
Example 3 — A recreational lifer bulking. Male, age 40, 180 cm, 90 kg, light activity (1.375), goal gain. BMR is about 1,830 kcal; maintenance is 1,830 × 1.375 ≈ 2,516 kcal. A 500 kcal surplus puts his target near 3,016 kcal/day, expected to add about 0.45 kg per week as he lifts.
FAQ
What is the difference between BMR and TDEE?
Your Basal Metabolic Rate (BMR) is the energy your body uses at complete rest to keep your heart beating, brain active and temperature steady — usually 60–70 percent of your daily burn. Total Daily Energy Expenditure (TDEE) multiplies BMR by an activity factor to add walking, exercise, work and daily movement. BMR is your floor; TDEE is what you actually eat from.
How accurate is the Mifflin-St Jeor calculator?
Mifflin-St Jeor is one of the most accurate equations for the average adult, typically within about 10 percent of measured lab values for healthy people. It is an estimate, not a metabolic chamber reading. The real test is two weeks of weighing yourself and tracking food: if the predicted number does not match the trend on the scale, nudge the Manual Adjustment slider up or down.
How many calories should I eat to lose weight?
Start with your maintenance TDEE and subtract about 500 kcal per day. For most people that targets roughly 0.45 kg (one pound) of loss per week. As a safety floor, women should generally not drop below about 1,200 kcal/day and men not below about 1,500 kcal/day without supervision, because very low intakes cost muscle and trigger rebound eating.
Will my metabolism slow down as I lose weight?
Yes, modestly. Two things happen: you weigh less, so your BMR falls, and your body adapts to the deficit over time. That is why maintenance should be recalculated every 5 kg or so, and why a smaller, consistent deficit usually beats an aggressive crash diet you cannot sustain.
Should I count every calorie forever?
No. Use this calculator and food tracking for a few weeks to learn portion sizes and how restaurant meals, snacks and drinks add up. Most people then switch to a rough, flexible estimate. Treat counting as a calibration tool, not a life sentence.
What activity level should I choose?
Be conservative. "Sedentary" is a desk job with little exercise; "light" is walking and one or two workouts a week; "moderate" is regular structured exercise; "active" is near-daily hard training; "very" is elite training or heavy physical labor. Most sedentary office workers should begin at sedentary or light, then raise it only after the scale confirms the slower trend.
Disclaimer
This calorie calculator is provided for informational purposes only and does not constitute medical, nutritional or dietetic advice. Estimates are based on the Mifflin-St Jeor equation and standard activity factors, which vary by body composition, genetics, medications, hormonal conditions and lifestyle. Pregnant or breastfeeding people, athletes in heavy training, and anyone with a medical condition such as diabetes or an eating disorder should consult a qualified healthcare professional or registered dietitian before changing their intake. Always adjust based on your own weight trend, energy levels and well-being.