Daily Iron Intake Calculator

Iron intake requirements vary significantly by age, sex, and physiological status. Iron is essential for hemoglobin synthesis, oxygen transport, and cellular energy metabolism. Both deficiency (the most common nutritional deficiency worldwide) and excess cause serious health consequences.

Dietary iron absorption formula: Absorbed Iron (mg) = Total Dietary Iron × Absorption Rate

Absorption rates:

• Heme iron (from meat, poultry, fish): 15–35% absorption
• Non-heme iron (from plants, fortified foods): 2–20% absorption
• With vitamin C (50+ mg concurrent): absorption increases 2–4×
• With calcium, tannins (tea/coffee), phytates (grains): absorption decreases 30–60%

Daily iron requirements (RDA, National Institutes of Health):

The calculator covers age 1 upward. The two infant rows are there for reference only, because infant iron is a feeding question rather than a dietary-target one: a breastfed baby draws on stores laid down before birth, and formula is already fortified. Ask a pediatrician rather than a calculator.

Tolerable upper intake level: 40 mg a day up to age 13, and 45 mg from 14 onward. That ceiling covers everything combined, food plus supplements. It exists because iron has no excretion route to speak of, so excess accumulates.

Iron deficiency anemia threshold: Hemoglobin < 12 g/dL (women), < 13 g/dL (men). Ferritin < 12 ng/mL confirms depleted iron stores.

Worked example: A 28-year-old vegetarian woman needs 18 mg/day (RDA). Non-heme iron lunch: 1 cup lentils (6.6 mg) + 1 cup cooked spinach (6.4 mg) = 13.0 mg total. Absorption without vitamin C: 13.0 × 0.08 = 1.04 mg absorbed With orange juice (70 mg vitamin C): the rate roughly triples, so 13.0 × 0.24 = 3.12 mg absorbed from exactly the same food.

Spinach is the classic trap here, and the Popeye story has a lot to answer for. A cup of cooked spinach genuinely contains 6.4 mg of iron, but it also carries oxalate, which binds that iron in the gut. Real-world absorption from spinach is poor even by non-heme standards. Lentils, tofu and pumpkin seeds are the better bet, and the orange juice matters more than the choice between them.