Audited —·Last updated 27 Jul 2026·5 citations·Tier 1·0 uses

Iron Intake Calculator

Calculate your daily iron needs by age, sex, pregnancy, and diet type. Uses IOM RDA values with vegetarian bioavailability adjustment.

Iron Intake Calculator

Biological sex
Pregnancy status
Vegetarian or vegan diet
Recommended dietary allowance
18
Absorption-adjusted target
32.4

Background.

Iron is an essential trace element that serves as the cofactor for oxygen transport, energy metabolism, DNA synthesis, and immune function. Approximately 70 percent of total body iron resides in hemoglobin and myoglobin, the proteins responsible for binding and delivering oxygen to tissues. Another 25 percent is stored as ferritin and hemosiderin in the liver, spleen, and bone marrow. The remaining fraction participates in enzymatic reactions involving cytochromes and peroxidases. Because the body has no active mechanism for iron excretion beyond basal losses in shed skin, intestinal mucosa, and menstrual blood, iron balance is maintained primarily at the level of intestinal absorption. The Iron Intake Calculator computes the Recommended Dietary Allowance for an individual based on age, sex, pregnancy status, and dietary pattern, using the official tables published by the Institute of Medicine and the bioavailability adjustments recommended by the National Institutes of Health.

The canonical use case is a premenopausal woman, a pregnant person, or a vegetarian who wants to know whether their diet provides sufficient iron to prevent deficiency. Iron deficiency is the most common nutritional deficiency worldwide, affecting an estimated 1.62 billion people globally and approximately 10 million in the United States. The prevalence is highest among women of reproductive age due to menstrual blood losses averaging 15 to 30 milligrams of iron per cycle, and among pregnant women because maternal blood volume expands by approximately 50 percent and fetal iron accretion requires 300 to 350 milligrams over gestation. Vegetarians and vegans are also at elevated risk because plant-derived non-heme iron has a fractional absorption of 2 to 20 percent compared to 15 to 35 percent for heme iron from meat, poultry, and fish.

The physiological context of iron metabolism explains why recommendations vary so dramatically across demographic groups. Adult men and postmenopausal women lose only about 1 milligram of iron per day through intestinal shedding and minor bleeding, so their RDA is set at 8 milligrams per day to cover these losses with a safety margin. Premenopausal women lose an additional 0.5 to 1.0 milligrams per day through menstruation, raising the RDA to 18 milligrams. During pregnancy, iron requirements surge to support erythrocyte mass expansion, placental growth, and fetal tissue development, pushing the RDA to 27 milligrams per day—the highest of any adult demographic. Lactation lowers the requirement to 9 milligrams per day because lactational amenorrhea reduces menstrual losses and because breast milk contains only 0.3 milligrams of iron per liter.

Bioavailability is the second major variable. The IOM based its RDAs on mixed diets containing both heme and non-heme iron sources. For individuals consuming exclusively plant-based diets, the absence of heme iron and the presence of absorption inhibitors such as phytates, polyphenols, and calcium reduce overall fractional absorption. The IOM and NIH both recommend multiplying the standard RDA by 1.8 for vegetarians to compensate for this bioavailability deficit. This adjustment is not a precise physiological constant but a population-level correction derived from absorption studies using radio-labeled iron tracers. The calculator applies this multiplier automatically when the user indicates a vegetarian or vegan diet.

What is iron intake calculator?

Iron is a transition metal, atomic number 26, that cycles between ferrous (Fe²⁺) and ferric (Fe³⁺) oxidation states to mediate electron transfer reactions. In nutrition, the term refers to dietary iron, which exists in two forms. Heme iron is bound to hemoglobin and myoglobin in animal muscle and organ tissues; it is absorbed directly into enterocytes via the HCP1 transporter and is relatively unaffected by meal composition. Non-heme iron is found in plants, fortified foods, and supplements; it is absorbed via the DMT1 transporter after reduction to Fe²⁺, and its absorption is strongly influenced by dietary enhancers such as ascorbic acid and inhibitors such as phytates and tannins. The human body contains approximately 3 to 4 grams of iron, most of which is recycled rather than excreted.

The standard unit for iron recommendations is milligrams of elemental iron per day. The calculator outputs values in milligrams. Valid age inputs cover 19 to 100 years, reflecting adult RDAs. The calculator does not compute pediatric or adolescent requirements, which follow different age brackets. Pregnancy status is limited to the three categories recognized by the IOM: not pregnant, pregnant, and lactating. The vegetarian adjustment applies to any diet lacking heme iron sources, including vegan, lacto-ovo vegetarian, and pescatarian diets if fish intake is minimal. Users should interpret the output as a dietary target, not a prescription for supplemental iron.

How to use this calculator.

  1. Enter your age in years.
  2. Select your biological sex.
  3. Select your current pregnancy or lactation status.
  4. Indicate whether you follow a vegetarian or vegan diet with little or no meat, poultry, or fish.
  5. Review your recommended iron intake in milligrams per day.
  6. Check the absorption-adjusted target if you selected a vegetarian diet.
  7. Compare the result to your typical diet or discuss it with a healthcare provider if you have symptoms of anemia such as fatigue or pallor.

The formula.

The calculator implements the Recommended Dietary Allowances published in the Institute of Medicine's 2001 Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. The RDAs are not continuous functions of age but step functions that change at demographic boundaries. For adults, the critical boundary is biological sex and, for women, pregnancy and menopausal status.

For males aged 19 and older and females aged 51 and older, the RDA is 8 milligrams per day. This value covers basal iron losses of approximately 1 milligram per day—0.6 milligrams from exfoliated gastrointestinal mucosal cells, 0.2 to 0.3 milligrams from skin and urine, and minor losses from hair and nails—with a coefficient of variation of 15 percent and an absorption efficiency of approximately 18 percent from a mixed diet. The IOM calculated the EAR at 6 milligrams and added two standard deviations to reach 8 milligrams, ensuring that 97.5 percent of the reference population maintains adequate iron stores.

For females aged 19 to 50 who are not pregnant or lactating, the RDA jumps to 18 milligrams per day. This higher value accounts for menstrual blood losses, which the IOM modeled as a log-normal distribution with a median of 0.51 milligrams of iron lost per day over the menstrual cycle. Because the distribution is right-skewed—some women experience heavy menstrual bleeding—the 97.5th percentile requirement is substantially higher than the median, driving the RDA upward. The EAR for this group is 8.1 milligrams, and the RDA is set at 18 milligrams to cover high-loss individuals.

Pregnancy triggers the highest RDA at 27 milligrams per day. The IOM partitioned pregnancy iron requirements into three components: maternal erythrocyte mass expansion requiring 450 milligrams, fetal and placental tissues requiring 270 milligrams, and basal losses over 280 days requiring 230 milligrams, totaling 950 milligrams. Assuming 25 percent absorption from a mixed diet and spreading over gestation, the EAR is 22.4 milligrams and the RDA is 27 milligrams. Lactation lowers the requirement to 9 milligrams because breast milk iron content is low and amenorrhea saves approximately 0.5 milligrams per day.

The vegetarian multiplier of 1.8 derives from absorption studies showing that non-heme iron absorption from plant-based diets averages 10 percent compared to 18 percent from mixed diets. Dividing 18 by 10 yields 1.8, meaning vegetarians must consume 80 percent more iron to absorb an equivalent amount. The calculator applies this multiplier to the base RDA when the user indicates a vegetarian diet.

A worked example.

Example

Consider a 28-year-old woman who is not pregnant, follows a vegetarian diet, and wants to know her iron target. The calculator first determines her base RDA. Because she is a female between 19 and 50 years old and not pregnant, the base value is 18 milligrams per day. Next, it checks her dietary pattern. Because she selected a vegetarian diet, the calculator applies the IOM bioavailability adjustment of 1.8, multiplying 18 by 1.8 to yield 32.4 milligrams per day. This is the absorption-adjusted target. For context, one cup of cooked lentils provides approximately 6.6 milligrams of non-heme iron, one cup of cooked spinach provides 6.4 milligrams, and one cup of fortified breakfast cereal can provide 18 milligrams. She would need to combine several iron-rich plant foods daily, ideally with vitamin C sources to enhance absorption, to approach 32.4 milligrams. A serum ferritin test would confirm whether her stores are adequate.

pregnancynot pregnant
sexfemale
vegetarianyes
age28

Frequently asked questions.

What is the difference between heme and non-heme iron?
Heme iron is bound to hemoglobin and myoglobin in animal foods such as beef, chicken, and fish. It is absorbed directly into intestinal cells and has a fractional absorption of 15 to 35 percent, largely independent of meal composition. Non-heme iron is found in plants, fortified cereals, and supplements. It must be reduced from ferric to ferrous iron before absorption and is strongly affected by dietary factors. Absorption ranges from 2 to 20 percent. The calculator's vegetarian adjustment exists because non-heme iron dominates in plant-based diets, requiring higher total intake to achieve equivalent absorption.
Can I take too much iron?
Yes. The Tolerable Upper Intake Level for elemental iron is 45 milligrams per day for adults. Chronic excess causes hemosiderosis, liver damage, and increased oxidative stress through Fenton chemistry. Acute iron overdose is a leading cause of poisoning death in children under 6. Iron supplements should not be taken unless deficiency is confirmed by blood tests, because the body lacks a regulated excretion pathway and stores accumulate progressively. Hemochromatosis, a genetic disorder of iron overload affecting approximately 1 in 300 people of Northern European descent, further increases toxicity risk.
What foods enhance iron absorption?
Vitamin C is the most potent enhancer, reducing ferric iron to the more soluble ferrous form and forming a chelate that remains soluble in the alkaline small intestine. Consuming 25 to 100 milligrams of vitamin C with a meal increases non-heme absorption two- to six-fold. Meat, fish, and poultry also contain the "meat factor," an unidentified compound that stimulates non-heme iron absorption. Organic acids such as citric, lactic, and malic acid have modest enhancing effects. Combining iron-rich plant foods with citrus fruits, tomatoes, or bell peppers at meals is a practical strategy for vegetarians.
What foods inhibit iron absorption?
Phytates in whole grains and legumes, polyphenols in tea and coffee, and calcium in dairy products all inhibit non-heme iron absorption. A cup of coffee consumed with a meal can reduce iron absorption by 35 to 60 percent. Calcium inhibits both heme and non-heme absorption, which is why the IOM recommends spacing calcium supplements away from iron-rich meals by at least two hours. The effects are most pronounced in single-meal studies; habitual diet patterns show partial adaptation over weeks as the gut upregulates absorption pathways.
Why do women need more iron than men?
Premenopausal women lose iron through menstrual blood. The average menstrual cycle expels 30 to 40 milliliters of blood, containing 15 to 30 milligrams of iron. Spread across a 28-day cycle, this adds approximately 0.5 to 1.0 milligrams of iron loss per day to the basal loss of 1.0 milligram shared by both sexes. Postmenopausal women and men have equivalent requirements because menstrual losses cease. Women with menorrhagia may lose significantly more and should be screened for iron deficiency annually. The higher RDA for premenopausal women reflects the 97.5th percentile of menstrual iron losses to cover virtually all women in the reference population.
Should pregnant women always take iron supplements?
Most prenatal vitamins contain 27 to 30 milligrams of iron, matching the pregnancy RDA. However, not all pregnant women need supplements if their diet is iron-rich and their pre-pregnancy stores are adequate. The World Health Organization recommends universal iron supplementation during pregnancy because deficiency is common and the consequences for fetal neurodevelopment are severe. Individual needs should be determined by prenatal care providers using hemoglobin and ferritin tests. Supplementation is particularly critical in the second and third trimesters when fetal iron demands peak.
Can I get enough iron from a vegan diet?
Yes, but it requires planning and attention to absorption enhancers. Vegan diets eliminate all heme iron, so total iron intake must be higher to compensate for lower absorption. Legumes, tofu, tempeh, dark leafy greens, fortified cereals, pumpkin seeds, and quinoa are good sources. Pairing these with vitamin C-rich foods at every meal maximizes absorption. Some vegans may need supplements if ferritin levels fall below 15 micrograms per liter. Regular monitoring of complete blood count and ferritin is advisable for vegetarians and vegans.
What are the symptoms of iron deficiency?
Early deficiency depletes ferritin stores without causing symptoms, which is why screening is important for at-risk groups. As deficiency progresses, anemia develops, producing fatigue, weakness, pale skin, shortness of breath on exertion, dizziness, cold extremities, brittle nails, and pica. In children, iron deficiency impairs cognitive development, attention span, and immune response. A complete blood count and serum ferritin test confirm diagnosis. Treatment typically involves dietary modification plus supplemental iron for three to six months. Intravenous iron is reserved for severe deficiency or malabsorption syndromes that prevent adequate oral supplementation.
Does cooking in cast iron increase dietary iron?
Yes. Acidic foods such as tomato sauce, chili, and applesauce leach small amounts of iron from cast iron cookware during cooking. The iron is inorganic and non-heme, but it contributes to total intake. Studies show that cooking acidic foods in cast iron can increase iron content two- to five-fold, though the absolute amount is modest—typically 1 to 5 milligrams per serving. It is not sufficient as a standalone strategy for treating deficiency but can be a useful adjunct for marginally deficient individuals.
Why is the lactation RDA lower than the non-pregnant female RDA?
Lactation requires only 9 milligrams per day because breast milk contains relatively little iron—about 0.3 milligrams per liter—and because lactational amenorrhea eliminates menstrual iron losses for several months. The body also increases iron absorption efficiency during lactation through upregulation of intestinal transporters. The lower RDA reflects these compensatory mechanisms. Postpartum women should still eat iron-rich foods to rebuild stores depleted by pregnancy, particularly if they plan to become pregnant again within two years. Delaying supplementation until after delivery is generally safe because newborns are born with sufficient iron stores for their first four to six months of life.

References& sources.

  1. [1]Institute of Medicine (2001). Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. National Academies Press.
  2. [2]National Institutes of Health, Office of Dietary Supplements (2023). Iron: Fact Sheet for Health Professionals.
  3. [3]Bothwell, T.H., Charlton, R.W., Cook, J.D., & Finch, C.A. (1979). Iron Metabolism in Man. Blackwell Scientific Publications. ISBN 978-0632004687
  4. [4]Hurrell, R. & Egli, I. (2010). Iron bioavailability and dietary reference values. American Journal of Clinical Nutrition 91(5):1461S-1467S. doi:10.3945/ajcn.2010.28674F
  5. [5]World Health Organization (2020). Guideline on Iron Supplementation in Postpartum Women.
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