Health Calculators
Iron needs.
Pick your age and life stage to see the daily iron Recommended Dietary Allowance and the upper limit, with the higher vegetarian target if it applies. Add what you take in to see the gap. Runs in your browser; nothing is sent anywhere.
Your details
Your iron target
Fill the form and press Calculate.
Worked example
A woman aged 19 to 50 on a vegetarian diet: the RDA is 18 mg, and 18 × 1.8 = 32.4 mg a day. If she gets 20 mg now, that is 20 ÷ 32.4 = 62% of the target with 12.4 mg to add. The upper limit for her is 45 mg.
How it works
Target = RDA, or RDA × 1.8 on a vegetarian diet. RDAs and upper limits (ULs) are the figures in the NIH Office of Dietary Supplements iron fact sheet, from the Food and Nutrition Board: for example 8 mg for men 19+, 18 mg for women 19 to 50, 8 mg for women 51+, 27 mg in pregnancy. The UL is 45 mg for ages 14 and up (including pregnancy and breastfeeding) and 40 mg for ages 1 to 13. Infants are left out; ask a pediatrician.
The 1.8 factor reflects the lower bioavailability of non-heme iron from plant foods. The fact sheet also notes experts recommend taking calcium and iron supplements at different times, and that iron can interact with levodopa, levothyroxine and acid-reducing medicines.
Sources (opened 2026-10-08): NIH Office of Dietary Supplements, Iron: Fact Sheet for Health Professionals (updated September 4, 2025).
FAQ
How much iron do I need per day?
It depends on age, sex and life stage. For adults 19 to 50 the RDA is 8 mg for men and 18 mg for women; it is 27 mg in pregnancy and 9 mg while breastfeeding. Women 51 and older need 8 mg.
Why do vegetarians need more iron?
The NIH fact sheet says the requirement is 1.8 times higher for people on vegetarian diets because iron from plant foods is absorbed less well. This tool multiplies the RDA by 1.8.
What is the upper limit for iron?
The Tolerable Upper Intake Level is 45 mg a day for ages 14 and up and 40 mg for children 1 to 13. High-dose iron supplements can cause stomach problems and, at extreme doses, serious harm.
Does this say whether I am iron deficient?
No. Only a blood test ordered by a clinician can show that. This is an intake target, not a diagnosis. Check with a pharmacist if you take medication, because iron interacts with some medicines.
Calcium can interfere with iron absorption, so tally it with the calcium intake calculator and read labels with the supplement label unit converter.
Disclaimer
Not medical advice. Upper limits are for adults and teens as listed; check with a pharmacist if you take medication. Do not take iron supplements without a clinician if you have hemochromatosis or are unsure of your iron status.