Daily Iron Intake Calculator — 8 mg, 18 mg or 27 mg

Iron is the nutrient where sex and life stage change the answer most: 8 mg a day for men, 18 mg for women aged 19 to 50, and 27 mg in pregnancy. Those are RDAs from the Dietary Reference Intakes. Pick your life stage below; the sections after it cover absorption, which matters as much as the target.

The RDA by life stage

Life stage	Iron per day
Children 4 to 8	10 mg
Ages 9 to 13	8 mg
Males 14 to 18	11 mg
Females 14 to 18	15 mg
Men 19 and older	8 mg
Women 19 to 50	18 mg
Women 51 and older	8 mg
Pregnancy	27 mg
Lactation, 19 to 50	9 mg

The tolerable upper intake level is 45 mg a day from age 14, and 40 mg below that. Note how close the 27 mg pregnancy target sits to it — one of the reasons prenatal iron dosing is a clinical decision rather than a shelf decision.

Two figures in the table surprise people. Lactation drops to 9 mg, lower than the non-pregnant 18, because menstruation is usually absent. And teen girls at 15 mg already need nearly double teen boys at 11 mg, from the year periods begin.

Heme and non-heme: absorption changes the arithmetic

Not all dietary iron is equally usable. Iron in meat, poultry and fish is largely heme iron and is absorbed efficiently; iron from plants is non-heme and is not, and its absorption swings widely with what else is on the plate.

The National Academies put a number on the consequence. Bioavailability from a mixed Western diet is estimated at about 18 percent, against roughly 10 percent from a vegetarian diet — and so, in the report’s own words, the requirement for iron is 1.8 times higher for vegetarians. A woman of 30 eating no meat is therefore working toward roughly 32 mg, not 18. Very restricted vegetarian diets can run lower still, near 5 percent absorption.

That multiplier is not a reason to reach for a supplement. It is a reason to eat iron-rich plants deliberately — lentils, beans, tofu, pumpkin seeds, fortified grains — and to pay attention to the next section, because meal composition moves non-heme absorption by more than the multiplier does. Plant-forward eating plans are covered on the vegetarian protein calculator.

What helps and what blocks

• Vitamin C in the same meal is the strongest practical enhancer of non-heme absorption. The daily vitamin C intake page has the targets.
• Coffee and tea contain polyphenols that inhibit it; move them an hour or two away from meals.
• Calcium competes with iron for uptake, so a large dairy load in the same meal works against it. The daily calcium intake numbers explain why that tradeoff is worth spacing out rather than skipping either nutrient.

The label says 18 mg for everyone

The FDA sets the Daily Value for iron at 18 mg, the highest common adult RDA, applied across the population over age 4. For an adult man whose requirement is 8 mg, a cereal listing 45% DV delivers 8.1 mg — his entire day’s iron, from a label that reads under half full. Convert to milligrams before comparing.

Deficiency, and the reason supplements need a test first

Not having enough iron is the most common cause of anemia, per MedlinePlus, and the symptoms are fatigue, pallor and breathlessness. The groups at risk are the ones with the higher targets: menstruating women, pregnant people and young children — the same groups the 2025–2030 Dietary Guidelines single out when they name iron a priority nutrient in adolescence and pregnancy.

The other direction is worse than most people assume. Excess iron is toxic, the upper limit is only 45 mg, and there is no efficient route for the body to excrete a surplus. “I’m tired, I’ll take iron” is exactly the reasoning to avoid — fatigue has many causes, and iron supplementation belongs after a blood test. Folate deficiency produces an anemia of its own and often travels with iron in pregnancy; see folic acid dosage during pregnancy.

This content is informational and does not replace evaluation by a physician. Iron supplementation requires professional guidance.