Iron Intake Calculator: Daily Recommended Amount (NIH)
Iron is an essential mineral that the body uses to produce haemoglobin, the protein in red blood cells that carries oxygen from the lungs to the rest of the body. It is also needed for myoglobin (a protein that provides oxygen to muscles), certain enzymes, normal immune function, and healthy neurological development. The body cannot produce iron on its own, so it must come entirely from diet or supplements. Iron from food comes in two forms: heme iron, found in animal products and absorbed at roughly 15 to 35 percent efficiency, and non-heme iron, found in plant foods and fortified products and absorbed at a much lower rate of 2 to 20 percent. The Recommended Dietary Allowance (RDA) for iron varies significantly by sex and life stage. Women of childbearing age require considerably more iron than men because of blood loss during menstruation. Pregnant people have the highest iron requirement at 27 mg per day. After menopause, women's requirements drop to match men's at 8 mg per day. This calculator shows your RDA for iron and the tolerable upper intake level. Always speak with a healthcare provider before taking iron supplements, as excessive iron can be harmful.
Your recommended daily iron intake is -- mg per day.
How iron absorption works
Iron absorption efficiency varies greatly depending on the type of iron and what you eat it with. Heme iron (from animal foods) is absorbed directly and is not significantly affected by other dietary factors. Non-heme iron absorption is influenced by many factors:
Heme iron absorption: approximately 15% to 35% of intake
Non-heme iron absorption: approximately 2% to 20% of intake
Vitamin C enhances non-heme absorption.
Calcium, phytates, and polyphenols (tea, coffee) reduce non-heme absorption.
Worked example
A 30-year-old woman (not pregnant or breastfeeding):
- Age group: 19 to 50 years, female
- RDA: 18 mg per day
- Tolerable upper limit: 45 mg per day
- From a 100 g serving of beef (approximately 2.6 mg iron): heme absorption at 25% = 0.65 mg absorbed
NIH Iron RDA table by age, sex, and life stage
| Life stage / Age | RDA (mg/day) | Upper limit (mg/day) |
|---|---|---|
| Infants 0 to 6 months | 0.27 (AI) | 40 |
| Infants 7 to 12 months | 11 | 40 |
| Children 1 to 3 years | 7 | 40 |
| Children 4 to 8 years | 10 | 40 |
| Boys 9 to 13 years | 8 | 40 |
| Girls 9 to 13 years | 8 | 40 |
| Boys 14 to 18 years | 11 | 45 |
| Girls 14 to 18 years | 15 | 45 |
| Men 19+ years | 8 | 45 |
| Women 19 to 50 years | 18 | 45 |
| Women 51+ years | 8 | 45 |
| Pregnant (14 to 18 years) | 27 | 45 |
| Pregnant (19 to 50 years) | 27 | 45 |
| Breastfeeding (14 to 18 years) | 10 | 45 |
| Breastfeeding (19 to 50 years) | 9 | 45 |
AI = Adequate Intake. All other values are RDAs. Source: NIH ODS Iron Fact Sheet for Health Professionals, 2024.
Tips for improving iron intake
Pairing non-heme iron sources with foods rich in vitamin C (citrus, bell peppers, strawberries, broccoli) significantly increases absorption. For example, eating iron-fortified cereal with orange juice or adding lemon juice to lentils can meaningfully increase the iron your body absorbs.
Vegetarians and vegans may need up to 1.8 times the standard RDA because plant-based iron is less bioavailable. This means a non-pregnant adult woman following a fully plant-based diet might aim for approximately 32 mg per day. Speak with a registered dietitian or healthcare provider for personalised guidance.
Iron calculator: frequently asked questions
How much iron do adults need per day?
According to the NIH, adult men aged 19 and older need 8 mg of iron per day. Women aged 19 to 50 need 18 mg per day, reflecting iron lost through menstruation. After menopause (51 and older), women's requirement drops to 8 mg per day. Pregnant people need 27 mg per day, the highest recommended intake, because iron demand increases substantially during pregnancy to support the growing fetus.
What is the tolerable upper intake level for iron?
The NIH sets the tolerable upper intake level (UL) for iron at 45 mg per day for adults aged 19 and older. Exceeding this level regularly can cause gastrointestinal distress, nausea, vomiting, and, in severe cases, organ damage. Iron toxicity is more likely from supplements than from food. Iron supplements should only be taken at doses above the RDA under medical supervision.
What is the difference between heme and non-heme iron?
Heme iron comes from animal sources (red meat, poultry, seafood) and is absorbed at a rate of approximately 15 to 35 percent. Non-heme iron comes from plant sources (legumes, fortified cereals, spinach, tofu) and is absorbed at a lower rate of approximately 2 to 20 percent. Consuming non-heme iron alongside vitamin C-rich foods improves absorption. Tea, coffee, calcium, and phytates found in whole grains can inhibit non-heme iron absorption.
Who is most at risk of iron deficiency?
Groups at higher risk of iron deficiency include women of childbearing age (especially those with heavy periods), pregnant people, infants and toddlers, vegetarians and vegans (due to lower absorption of non-heme iron), frequent blood donors, and people with certain gastrointestinal conditions (coeliac disease, Crohn's disease) that impair absorption. Iron deficiency anaemia is the most common nutritional deficiency worldwide, according to the NIH.
How do I know if I am iron deficient?
The only reliable way to diagnose iron deficiency is through blood tests ordered by a healthcare provider. Common tests include serum ferritin (the most sensitive early indicator), haemoglobin, haematocrit, and serum iron. Symptoms of iron deficiency can include fatigue, weakness, pale skin, shortness of breath, dizziness, cold hands and feet, and brittle nails, but these symptoms overlap with many other conditions. Do not self-diagnose or self-treat with high-dose iron supplements without medical advice.
Official sources
- NIH Office of Dietary Supplements: Iron Fact Sheet for Health Professionals.
- NIH Office of Dietary Supplements: Iron Fact Sheet for Consumers.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology. General information only, not medical advice.