How many calories do I need a day? Mifflin-St Jeor with examples

Most adults need roughly 1,600–2,400 kcal a day (women) or 2,000–3,000 kcal (men), depending on age and activity. The NHS uses 2,000 and 2,500 as averages. To get your own number, estimate your resting burn with the Mifflin-St Jeor formula, then multiply by an activity factor. This guide shows both steps with worked examples.

The Mifflin-St Jeor formula

Mifflin-St Jeor estimates the calories your body burns at rest. It was published in 1990 from measurements on 498 healthy adults and is still widely used by dietitians.

• Men: 10 x weight (kg) + 6.25 x height (cm) - 5 x age (years) + 5
• Women: 10 x weight (kg) + 6.25 x height (cm) - 5 x age (years) - 161

To use pounds and inches, divide pounds by 2.205 for kg and multiply inches by 2.54 for cm. A systematic review of four common equations found Mifflin-St Jeor the most reliable, predicting resting metabolic rate within 10% of measured in more people than the others. It can still be off for an individual, especially at very high or low body fat.

Step 2: multiply by your activity level

Resting burn is not what you spend over a whole day. The FAO/WHO/UNU expert report uses a physical activity level (PAL) multiplier:

Lifestyle	PAL multiplier
Sedentary or light activity	1.40–1.69
Active or moderately active	1.70–1.99
Vigorous	2.00–2.40

Some online calculators use a lower multiplier such as 1.2 for "sedentary". The FAO table starts at 1.40, even for the least active free-living lifestyles, so a lower factor tends to underestimate.

Worked examples

Person	Resting burn (Mifflin-St Jeor)	x 1.4	x 1.7
Woman, 35, 165 cm (5 ft 5 in), 65 kg (143 lb)	1,345 kcal	1,880 kcal	2,290 kcal
Man, 40, 180 cm (5 ft 11 in), 85 kg (187 lb)	1,780 kcal	2,490 kcal	3,030 kcal
Woman, 52, 160 cm (5 ft 3 in), 72 kg (159 lb)	1,299 kcal	1,820 kcal	2,210 kcal

Worked through for the first woman: 10 x 65 = 650, plus 6.25 x 165 = 1,031, minus 5 x 35 = 175, minus 161 gives 1,345 kcal. Times 1.4 is 1,883.

Compare with the Dietary Guidelines for Americans (2020–2025), which list 1,800 / 2,000 / 2,200 kcal for women aged 31–35 (sedentary / moderately active / active) and 2,400 / 2,600 / 2,800 for men aged 36–40. The formula gives a personal answer; the table gives a sanity check.

What counts as moderately active?

The Dietary Guidelines define the levels this way. Sedentary means only the activity of independent living. Moderately active adds physical activity equal to walking about 1.5 to 3 miles a day at 3 to 4 mph. Active means the equivalent of walking more than 3 miles a day at that pace. Be honest: a desk job plus a gym session three times a week is usually closer to light or moderate than to very active.

Needs also fall with age. For sedentary adults the guidelines list 2,000 kcal for women aged 19–25, 1,800 at 26–50 and 1,600 from 51 on, and 2,600 kcal for men aged 19–20, 2,400 at 21–40, 2,200 at 41–60 and 2,000 from 61.

How to use your number

• To maintain weight: eat close to your estimate.
• To lose weight: eat somewhat below your estimate; a modest gap is easier to keep than a crash diet. Do not go under 1,200 kcal (women) or 1,500 kcal (men) without a doctor or dietitian.
• To gain muscle: eat a little above your estimate, with enough protein and strength training.

Weight changes slowly. A modelling study in The Lancet found that body weight responds to a change in intake with a half-time of about a year, so a fixed calorie gap does not keep producing the same loss week after week. Judge your target by the trend over a few weeks, not by day-to-day swings, and adjust in small steps.

Why your number is an estimate

Formulas do not know your muscle mass, sleep, health conditions or how much you fidget. If you are pregnant or breastfeeding, a teenager, over 65, or managing diabetes or another medical condition, talk to your doctor or dietitian about your needs.

Tracking it in practice

Knowing your target is half the work; the other half is knowing what you eat. During setup, Tabaq sets a daily calorie target from your age, height, weight, activity and goal, and you can change it. Photograph a meal and Tabaq estimates the portion, and you can edit the weight if it is off. Start your 3-day trial and compare a typical day with your number.