TDEE & Calorie deficit calculator

How this calorie calculator works

The calculator follows three steps – the same ones the NutriSmart app uses to set your daily goal, so the numbers match if you continue in the app.

1. Basal metabolic rate (BMR). We use the Mifflin-St Jeor equation, which a systematic review found to be the most accurate of the common formulas for healthy adults (Frankenfield et al., 2005; Mifflin et al., 1990):

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

2. Total daily energy expenditure (TDEE). BMR is multiplied by an activity factor:

Activity level	Factor	Typical day
Sedentary	1.2	Desk job, little or no exercise
Lightly active	1.375	Light exercise 1–3 days a week
Moderately active	1.55	Exercise 3–5 days a week
Very active	1.725	Hard exercise 6–7 days a week
Extremely active	1.9	Physical job or training twice a day

3. Your goal. To lose weight, the calculator takes 10–30% off your TDEE; to gain weight or build muscle, it adds 10–30%. To maintain, your target is simply your TDEE.

Example

A 30-year-old woman, 165 cm (5 ft 5 in) and 68 kg (150 lb), lightly active, who wants to lose weight at the standard pace:

• BMR = 10 × 68 + 6.25 × 165 − 5 × 30 − 161 = 1,400 kcal
• TDEE = 1,400 × 1.375 = 1,925 kcal – this is her maintenance
• Target = 1,925 × 0.80 = 1,540 kcal a day

That is a deficit of about 385 calories a day, or roughly 0.35 kg (0.8 lb) a week at the start.

How big should your calorie deficit be?

A deficit of 10–20% suits most people: it is large enough to see progress on the scale within a few weeks and small enough to keep your energy, training and mood steady. Faster paces (25–30%) work for some people for a short time, but hunger and muscle loss rise with the size of the deficit.

Two things to keep in mind:

• Don’t go too low. Harvard Health advises that calorie intake should not fall below about 1,200 a day for women or 1,500 for men except under the supervision of a health professional (Harvard Health). The calculator warns you when your target is below that.
• Weight loss slows down over time. The classic “7,700 kcal per kg (3,500 per lb)” rule we use for the weekly estimate is only accurate at the start. As you get lighter, you burn less, so progress naturally slows (Hall et al., 2011). Recalculate every 4–5 kg (10 lb) you lose.

From calories to a daily plan

Calories decide whether you lose or gain weight; what those calories are made of decides how you feel and how much muscle you keep. Under the main number, the calculator splits your target into protein, carbs and fat. For more detail, see the macro calculator and the protein calculator. To check whether your weight is in the healthy range, use the BMI calculator.

The hard part is not the maths – it’s hitting the number every day. That’s what NutriSmart is for: snap a photo of what you eat or scan a barcode and it counts the calories and macros for you against these same targets.

When to recalculate

• Every 4–5 kg (10 lb) of weight change.
• When your activity changes – a new job, a new training plan, an injury.
• If your weekly average weight hasn’t moved for 3 weeks despite tracking carefully.

This calculator is for healthy adults aged 18–80. It isn’t suitable during pregnancy or breastfeeding, for people with eating disorders, or for medical conditions that affect metabolism – talk to your doctor or a registered dietitian in those cases.