Calorie calculator: maintenance, target and macros

Written by Norbert Grzenkowicz · 15 October 2026

The calorie calculator estimates resting energy expenditure with the Mifflin-St Jeor equation, multiplies it by one of five common activity multipliers (1.2 to 1.9) and takes off or adds a percentage for your goal. From that target it sets protein (2.2 g per kg of body weight), fats (25% of the target) and carbs from what is left. It is an estimate: the test is your weight trend over 2-3 weeks.

Work out your calories and macros

Enter your details. The result updates as you type; the calculator is free and needs no account.

The calculator needs JavaScript. The formulas are written out below, so you can work them by hand.

What the calculator does, step by step

Resting energy expenditure (Mifflin-St Jeor): 10 × weight in kg + 6.25 × height in cm - 5 × age in years, plus 5 for men or minus 161 for women.
Maintenance: step 1 times an activity multiplier of 1.2, 1.375, 1.55, 1.725 or 1.9.
Calorie target: maintenance minus or plus the percentage you enter (by default -20% for a cut, +10% for a bulk).
Protein: 2.2 g for every kilogram of body weight.
Fats: 25% of the calorie target, divided by 9 kcal per gram.
The rest: the calorie target minus protein (4 kcal per gram) and fats, divided by 4, is your carbs.

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Mifflin-St Jeor was derived from measurements of 498 healthy adults aged 19 to 78, both normal weight and obese. In the same study, the 1919 Harris-Benedict equations overestimated measured resting expenditure by 5%.

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How to pick your activity level

The activity multiplier turns resting expenditure into your whole day's maintenance. The calculator uses five levels that are common in calorie calculators. It is a convention, not the result of one study. The multipliers and training days in the table are as printed in Sheridan College's teaching calculator.

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The calculator's five activity levels
Level	Multiplier	Who it fits	Multiplier vs FAO ranges
Sedentary	1.2	Desk job, no training	Below 1.40
Lightly active	1.375	Training 1-3 days a week	Below 1.40
Moderately active	1.55	Training 3-5 days a week	1.40-1.69
Very active	1.725	Training 6-7 days a week, or a physical job	1.70-1.99
Extra active	1.9	Hard physical job plus training, or training twice a day	1.70-1.99

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The sourced reference point for this scale is the 2004 FAO/WHO/UNU report. It sorts adult lifestyles into three PAL ranges, PAL being total daily energy expenditure divided by basal metabolic rate: sedentary or light 1.40-1.69, active 1.70-1.99, vigorous 2.00-2.40. Its example office worker's day, with an hour of driving and an hour of walking, comes to 1.53. The two lowest multipliers sit below those ranges. The report says free-living adults sustain a PAL of about 1.40 to 2.40, and treats a value around 1.2 as fitting only totally inactive people. With a desk job, 1.2 and 1.375 may therefore underestimate you. The comparison is approximate: PAL is measured against basal metabolic rate, while the calculator multiplies the Mifflin-St Jeor result.

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The report says an hour of moderate or vigorous exercise a day takes a desk worker's PAL from about 1.55 to 1.75. If you sit at work and lift 3 times a week, you average less than an hour of exercise a day, so do not start at very active. The calculator starts at 1.375, the level for training 1-3 days a week. Run 1.55 as well and treat the two answers as a range your weight will narrow down; by the FAO report you are more likely near the top of it.

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Where the default numbers come from

The calculator's defaults and their sources
Setting	Value	Basis
Protein	2.2 g/kg	Morton et al. 2018: gains in fat-free mass level off at about 1.62 g/kg a day (95% CI 1.03-2.20), so the authors suggest about 2.2 g/kg for lifters who want to maximise them.
Fats	25% of calories	Inside the 15-30% of calories in Helms et al. (contest prep), the 20-30% in Ruiz-Castellano et al. (fat loss phase) and the 20-35% in Iraki et al. (off-season).
Bulk	+10%	The low end of a surplus of about 10-20% above maintenance for novice and intermediate lifters (Iraki et al. 2019); the authors advise advanced lifters to use less.
Cut	-20%	The sources set the rate, not a percentage: 0.5-1% of body weight a week. For 80 kg and a maintenance of 2,500-2,800 kcal, 20% less is 500-560 kcal a day, about 0.6% of body weight a week by the rule of thumb in Helms et al. (500 kcal a day is about 1 lb, 0.45 kg, a week).

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For a cut, the sources give more protein: 2.2-3.0 g/kg in the Ruiz-Castellano et al. review, and 2.3-3.1 g/kg in the ISSN position stand for resistance-trained people in a deficit. 2.2 g/kg is the bottom of the first range. If you want more, work protein out by hand and take the extra calories off your carbs.

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Example: 80 kg, on a cut

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What the calculator cannot know

Differences between people. In Mifflin et al., the equation from weight, height, age and sex explained 71% of the differences in resting expenditure (R² 0.71), and fat-free mass alone 64%. Your own expenditure can sit well above or below the result.
Your activity. The multiplier is one of five conventional levels, not a measurement of your week.
How accurately you log. The calculator turns kcal into grams with the same factors as EU food labels (4, 9 and 4 kcal/g). If your logging is off, the weight trend tests a different number from your target.

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How to check the result on the scale

Eat to the calculator's target and weigh yourself every morning under the same conditions.
Take the 7-day average and compare it week to week. After 3 weeks you have two comparisons instead of one.
On a cut, aim to lose 0.5-1% of body weight a week (Helms et al., Ruiz-Castellano et al.). On a bulk, as a novice or intermediate, aim to gain 0.25-0.5% a week (Iraki et al.).
If the rate is outside that range, change your calories. By the rule in Helms et al. (500 kcal a day is about 0.45 kg a week), 0.1 kg a week is about 110 kcal a day. It is an approximation, so watch the trend for another 2-3 weeks after each change.

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How CalXd does it

CalXd calculates your daily calorie and macro targets from your profile and your goal: cut, bulk or maintain.

You log your weight in the app and see it on a chart with a 7-day average line. At most once every 7 days, CalXd reads your weight trend over the last 3 weeks and, when there is enough data, suggests a new calorie target that you decide whether to apply. The first suggestion comes no earlier than 4 weeks into a goal. You can also set the calorie target yourself; CalXd then suggests no changes.

Questions

Is this calorie calculator free?

Yes. The calculator on this page is free, needs no account and no app, and runs in your browser. The formulas are written out above, so you can repeat the sums by hand.

How accurate is an online calorie calculator?

It gives an estimate. Mifflin-St Jeor explained 71% of the differences in resting expenditure between the people measured, and the activity level is a choice between five conventional levels. Your real maintenance shows up only in your average weight over 2-3 weeks of eating to the result.

How many calories should I eat on a cut or a bulk?

Reviews for lifters set a rate rather than a fixed number: on a cut, 0.5-1% of body weight a week; on a bulk (novice and intermediate), 0.25-0.5% a week from a surplus of about 10-20%. The calculator starts at -20% and +10%, and you adjust from your weight trend.

Why is protein set from body weight, not from calories?

Because studies give the need in grams per kilogram of body weight, for example about 2.2 g/kg in the Morton et al. meta-analysis. When you change the calorie target, protein stays, fats move by a quarter of the change and carbs take the rest.

Does the calculator work for under-18s?

No. It accepts ages 18 to 80: Mifflin-St Jeor was derived from adults aged 19 to 78, and the macro sources are about adults who lift.

Sources

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