From the Guidelines

The daily caloric requirement per unit of body weight is approximately 25-35 kcal/kg.

The recommended energy intake varies based on factors such as age, sex, level of physical activity, body composition, weight status goals, and presence of illness or inflammation 1.
For older persons, a guiding value for energy intake is 30 kcal/kg body weight per day, which should be individually adjusted based on nutritional status, physical activity level, disease status, and tolerance 1.
In patients with specific conditions such as cancer, surgery, or critically ill patients, energy requirements may vary and should be estimated using indirect calorimetry or weight-based formulas 1.
For polymorbid medical inpatients, total energy expenditure can be estimated at approximately 27 kcal/kg actual body weight per day, with resting energy expenditure estimated at 18-20 kcal/kg actual body weight per day 1.
Severely underweight patients may require 30 kcal/kg actual body weight per day, which should be achieved cautiously and slowly to avoid refeeding syndrome 1.

Indirect calorimetry is the most accurate method for estimating energy expenditure, but weight-based formulas can be used as a starting point in its absence 1.
Activity or stress factors should be added to resting energy expenditure to estimate total energy expenditure 1.
Nutritional targets should be individualized based on patient-specific factors, and input from a healthcare professional, such as a dietitian, is essential for adequate assessment of nutritional needs 1.

From the Research

The daily caloric requirement per unit of body weight can be estimated based on various factors, including age, sex, weight, and activity level.

A study published in the Journal of the American Dietetic Association in 1982 proposed an estimate of 50 kcal per kilogram lean body mass (LBM) per day for light activity 2.
Another study published in The American Journal of Clinical Nutrition in 2014 found that the total daily energy expenditure (TDEE) for nonobese men and women was approximately 2443 ± 397 kcal/d, with a mean TDEE of 20% higher in men than in women 3.
The same study also provided a regression equation relating mean TDEE to demographics and weight: TDEE (kcal/d) = 1279 + 18.3 (weight, kg) + 2.3 (age, y) - 338 (sex: 1 = female, 0 = male) 3.

Several factors can affect an individual's daily caloric requirements, including:

Body composition: A study published in the International Journal of Obesity in 2008 found that a larger cumulative energy deficit is required per unit weight loss for people with greater initial body fat 4.
Sex: The same study found that men can lose more weight than women for a given energy deficit since women typically have more body fat than men of similar body weight 4.
Age: The study published in The American Journal of Clinical Nutrition in 2014 found that age is a significant factor in determining TDEE, with older adults having lower energy requirements 3.
Physical activity: The Dietary Guidelines for Americans recommend creating an energy deficit of at least 500 kcal a day to facilitate weight loss, which can be achieved through a combination of diet and physical activity 5.

Estimating daily caloric requirements can be complex and may require individualized assessments.

A study published in the Journal of the Academy of Nutrition and Dietetics in 2019 found that most respondents accurately reported typical daily calorie needs for a person of their sex, age group, and physical activity level, but distinct differences emerged between demographic groups 6.
The study published in The American Journal of Clinical Nutrition in 2014 provided a regression equation that can be used to estimate the free-living caloric requirements of nonobese adults 3.