James Smith Calculator
Find your TDEE, daily calorie target and macro breakdown in under 2 minutes. Based on the revised Harris-Benedict formula (Roza & Shizgal, 1984). No account or email required.
What’s your goal?
Your personal stats
Between 15 and 80
e.g. 178 cm = 5 ft 10 in
How active are you?
Be honest — most people are one level lower than they think.
Your results
Calories burned at complete rest. Eating below this long-term is not recommended.
Total daily burn including activity. Eat here to maintain your current weight.
Your personalised daily calorie target based on your goal.
Your Macro Targets
Protein-first approach (2 g per kg bodyweight). Adjust to your food preferences.
Preserves muscle during a deficit and keeps you full. Prioritise this macro above all others.
Primary fuel source for energy and training performance. Fill remaining calories here.
Essential for hormones, joint health and absorbing fat-soluble vitamins (A, D, E, K).
BMI
Note: BMI is a blunt metric that does not account for muscle mass. A muscular person may show as “overweight” while being perfectly healthy. Treat it as one data point, not a verdict.
These figures are estimates based on the revised Harris-Benedict formula (Roza & Shizgal, 1984). Individual results vary. This is a starting point — not medical advice. Track your intake and actual weight for 2 weeks and adjust if needed. Consult a healthcare professional if you have specific dietary requirements or health conditions.
What Is the James Smith Calculator?
The James Smith Calculator is a free tool that calculates your TDEE (Total Daily Energy Expenditure), personalised daily calorie target and macro breakdown — all based on the approach popularised by James Smith, one of the UK’s most well-known personal trainers and nutrition coaches.
Unlike generic calorie calculators that give you a single number with no context, this tool calculates your BMR, applies an activity multiplier, adjusts for your specific goal (fat loss, maintenance or muscle gain), and then splits those calories into protein, carbs and fats using a protein-first methodology. The result is a complete picture of what to eat — not just a number to hit.
The formulas are based on the revised Harris-Benedict equation published by Roza and Shizgal in 1984 — the most widely validated BMR prediction formula available for the general population.
How to Use the James Smith Calculator
The calculator walks you through four steps, takes under two minutes, and requires no account, no email and no app download.
- Choose your goal — Lose fat, maintain weight, or gain muscle. This determines how your calorie target is adjusted from your TDEE.
- Enter your stats — Gender, age, height and weight. Toggle between metric (cm, kg) and imperial (ft/in, lbs) using the buttons above each input.
- Select your activity level — Five options from sedentary to extremely active, each with a plain-English description. Be honest here — most people who exercise 3–4 times a week but sit at a desk all day are in the “moderately active” category, not “very active.”
- View your results — BMR, TDEE, daily calorie target and full macro breakdown appear instantly. Results are saved to your browser so they’re there when you return.
What Is TDEE and Why Does It Matter?
TDEE stands for Total Daily Energy Expenditure — the total number of calories your body burns across an entire day. It is made up of your Basal Metabolic Rate (the energy used at rest) multiplied by an activity factor that accounts for everything you do during the day: walking, working out, even fidgeting.
TDEE matters because it is the anchor for every calorie decision you make. Without knowing it, you are guessing. Most people who struggle to lose weight are eating at or above their TDEE without realising it — not because they eat “badly”, but because they don’t know their actual maintenance number.
Once you know your TDEE, fat loss becomes simple maths: eat consistently below it. How far below is where the nuance lies — and why a sustainable 20% deficit beats aggressive restriction every time. For a full explanation of this approach, read: Calorie Deficit for Fat Loss — What James Smith Gets Right.
How Are Your Macros Calculated?
The calculator uses a protein-first approach:
- Protein: 2 g per kg of bodyweight (rounded to the nearest 5 g). At 4 kcal per gram, this is calculated first and allocated directly from your calorie target.
- Fats: 25% of total daily calories, divided by 9 (kcal per gram of fat). Fat is kept at a healthy fixed percentage rather than being squeezed out in the name of “cutting calories.”
- Carbohydrates: All remaining calories divided by 4 (kcal per gram of carbohydrate). Carbs fill the rest — and contrary to popular belief, carbohydrates do not cause fat gain. Excess calories do.
Protein is the macro with the most evidence behind it for body composition. Hitting your protein target while in a calorie deficit preserves muscle, keeps you full, and improves the quality of weight you lose. For a deeper breakdown of how macros work, read: James Smith Macro Calculator Explained.
James Smith Calculator vs Other Calorie Calculators
There are dozens of TDEE calculators online. Here is how this one compares to the most common alternatives:
| Feature | James Smith Calculator | MyFitnessPal | Generic TDEE sites |
|---|---|---|---|
| Formula used | Revised Harris-Benedict (1984) | Mifflin-St Jeor | Varies |
| Macro breakdown | ✓ Protein-first methodology | ✓ Adjustable but generic | Rarely |
| Goal adjustment | ✓ 20% deficit / lean surplus | Fixed 500 kcal deficit | Varies |
| Account required | ✓ No | Yes | Usually no |
| BMI included | ✓ With plain-English note | No | Some |
| Imperial/metric toggle | ✓ | ✓ | Varies |
| Saves results locally | ✓ Browser localStorage | Account only | No |
Frequently Asked Questions
The James Smith Calculator is a free online tool that calculates your TDEE (Total Daily Energy Expenditure), daily calorie target and full macro breakdown — protein, carbs and fats — based on the principles James Smith teaches. It uses the revised Harris-Benedict formula and requires no sign-up or email address.
The calculator uses the revised Harris-Benedict formula — the most widely validated TDEE prediction equation available. Like all formulas, it produces an estimate, not a perfect measurement, as individual metabolic rates vary. Use the result as a starting point, track for two weeks, and adjust by 100–150 kcal based on real results.
TDEE stands for Total Daily Energy Expenditure — the total calories your body burns over 24 hours, including your Basal Metabolic Rate (BMR) plus all activity. Eating at your TDEE maintains your weight. Eating below it creates a deficit for fat loss; eating above it creates a surplus for muscle gain.
The James Smith approach recommends a 20% deficit below your TDEE. This creates a sustainable rate of fat loss — roughly 0.5 to 1% of bodyweight per week — without the muscle loss or metabolic slowdown that comes with extreme restriction. For a TDEE of 2,500 kcal, a 20% deficit means eating 2,000 kcal per day.
BMR stands for Basal Metabolic Rate — the calories your body burns at complete rest just to sustain basic functions: breathing, circulation, organ activity and body temperature. It is the minimum energy your body needs to survive. Eating consistently below your BMR long-term leads to muscle loss, hormonal disruption and metabolic adaptation.
The calculator uses a protein-first approach: protein is set at 2 g per kg of bodyweight (4 kcal/g), fats are set at 25% of total daily calories (9 kcal/g), and the remaining calories are allocated to carbohydrates (4 kcal/g). For example, an 80 kg person targeting 2,000 kcal/day would get approximately 160 g protein, 56 g fat and 220 g carbs.
Yes. The calculator uses gender-specific versions of the Harris-Benedict formula, accounting for the differences in average muscle mass and resting metabolic rate between males and females. Select “Female” in step 2 and the correct formula is applied automatically.
Recalculate every 4 to 6 weeks, or whenever your weight changes by more than 5 kg. As your body composition changes, so do your calorie and macro needs. A lighter body burns fewer calories, so your deficit target will naturally decrease as you lose weight.
Related Reading
Go deeper on the principles behind the calculator: