Variable Definitions

• A = Age in years
• W = Weight in kilograms (lbs × 0.4536)
• H = Height in meters (total inches × 0.0254)
• PA = Physical Activity coefficient (see table below)
• +20 / +25 = Energy deposition for growth (children/adolescents)

Activity Level Definitions

• Only light physical activity associated with typical daily life (e.g., household tasks, walking to the car).
• Physical activity equivalent to walking about 1.5 to 3 miles per day at 3 to 4 mph, in addition to daily activities.
• Physical activity equivalent to walking more than 3 miles per day at 3 to 4 mph, in addition to daily activities.
• Hard exercise or physical labor most of the day, equivalent to walking about 17 miles per day at 3 to 4 mph (e.g., competitive athletes, construction workers).

Under the NASEM 2023 equations

Switching the calculator to NASEM 2023 changes the shape of the adjustment, not just its size. Pregnancy is no longer a fixed amount added on: the 2023 report publishes its own regression for each activity level (Table 5-17), carrying a gestational-week term and an energy-deposition term banded by BMI. The increase therefore moves with your age, body size and activity instead of always being +340.

Lactation still adds a fixed amount under the 2023 equations, but with its own published constants (Tables 5-18 and 5-19): for adults, +400 kcal/day for 0 to 6 months and +380 kcal/day for 7 to 12 months. The first figure is 540 kcal of milk production less 140 kcal mobilized from your own stores. For girls 14 to 18 it is +380 and +360: their tables leave out the 20 kcal a day their usual estimate adds for growth.

The calculator asks which trimester you are in, not which week, so it evaluates the gestational-week term at each trimester's midpoint: week 20 and week 34, the same two weeks IOM 2005 used to derive the +340 and +452 above. Energy deposition is banded from the height and weight you enter, which stands in for pre-pregnancy BMI.

Life Stage Groups

DRI values are organized into 20 life stage groups based on age, sex, and pregnancy/lactation status. The calculator maps your profile to the appropriate group:

Reference Value Types

• EAR, Estimated Average Requirement: the average daily intake estimated to meet the needs of half of the healthy individuals in a group. It is used to assess the diets of groups, and the RDA is set from it.
• RDA, Recommended Dietary Allowance: the average daily intake sufficient to meet the nutrient requirements of nearly all (97 to 98%) healthy individuals in a group.
• AI, Adequate Intake: the recommended average daily intake based on observed or experimentally determined approximations. Used when an RDA cannot be determined.
• UL, Tolerable Upper Intake Level: the highest average daily nutrient intake level likely to pose no risk of adverse health effects to almost all individuals.
• CDRR, Chronic Disease Risk Reduction Intake: intake level above which reducing intake is expected to lower chronic disease risk.
• AMDR, Acceptable Macronutrient Distribution Range: the range of intake for an energy source (carbohydrate, fat) associated with reduced risk of chronic disease while providing adequate intakes of essential nutrients. Expressed as a percentage of total calories, then converted to grams using your estimated calorie needs.

Macronutrient Calculations

Carbohydrate and fat recommendations are shown as gram ranges calculated from AMDRs. For example, the carbohydrate AMDR for adults is 45 to 65% of total calories. At 2,400 kcal/day: (2400 × 0.45) / 4 = 270g minimum, (2400 × 0.65) / 4 = 390g maximum. Water and the fatty acids use the fixed AI values from the DRI tables.

Carbohydrate never goes below its RDA: 130 g a day from age 1, 175 g in pregnancy and 210 g while breastfeeding. For a small child, 45% of calories can come to less, so the range starts at the RDA.

Protein and fiber

Protein is your body weight in kilograms times the RDA per kilogram for your life stage. Example: 170 lb is 77.1 kg, and 77.1 × 0.8 = 62 g.

The published pregnancy value covers the second half of pregnancy; before that, the value for adults applies. The calculator asks for a trimester and places the 2nd at week 20, where the second half begins.

Fiber is 14 g for every 1,000 calories of your estimated energy requirement, at every age. Example: at 2,803 kcal/day, 2,803 × 14 / 1,000 = 39 g.

These are the rules the USDA's DRI Calculator for Healthcare Professionals uses. For the same person, protein and the recommended vitamin and mineral amounts come out the same, and calories and fiber do too with the NASEM 2023 equations.

Source: IOM (2006), Dietary Reference Intakes: The Essential Guide to Nutrient Requirements, Protein and Amino Acids, Table 1; Fiber, Table 1.