Iron carries oxygen in the blood. Women before menopause, pregnant women and frequent blood donors need more. Take it only if you know you need it.
Calculator Official intake Study doses Best form Works with Safety Sources
PRI (population reference intake)
| Men | 11 mg |
|---|---|
| Women 18-50 | 16 mg |
| Women 51+ | 11 mg |
| Pregnancy | 16 mg |
| Breastfeeding | 16 mg |
Safe level: 40 mg a day
EFSA could not set a safe limit for iron, so 40 mg is a "safe level of intake". It does not apply to iron prescribed for deficiency.
Women: 16 mg before menopause, 11 mg after. PillMath uses age 51+ as a stand-in for after menopause.
Source: EFSA 2017 · EFSA 2025 · EFSA NDA Panel 2024
RDA (recommended dietary allowance)
| Men | 8 mg |
|---|---|
| Women 18-50 | 18 mg |
| Women 51+ | 8 mg |
| Pregnancy | 27 mg |
| Breastfeeding | 9 mg |
Safe upper limit: 45 mg a day
Source: National Academies (NASEM) 2019
These are doses tested in research, not personal advice. Some exceed the upper limit because they were short courses or given under medical care.
60 mg every other day
In women with depleted iron, 60 mg every other day was absorbed better than 60 mg every day (about 22% vs 16%), and splitting a dose in two did not help. Treating anaemia needs a doctor.
80 mg a day
198 menstruating women with unexplained fatigue, ferritin under 50 µg/L and normal haemoglobin took 80 mg iron a day or placebo for 12 weeks. Fatigue fell 48% vs 29%. Get ferritin tested first: this is above the EFSA safe level.
Best form
Ferrous sulfate, salt weight (~20% Fe)
Why: Ferrous forms (sulfate, fumarate, gluconate) are absorbed better than ferric forms. Ferrous sulfate is the most widely used form and was the form in the key absorption trials.
Alternatives: Up to 4 in 10 people get stomach side effects from ferrous salts. Iron bisglycinate and other newer forms give comparable blood results with fewer complaints, so they are a fair swap if sulfate upsets you. Whatever the form, every other day in the morning, away from tea, coffee and calcium, absorbs best.
Stoffel NU et al. 2017 · NIH Office of Dietary Supplements 2026 · Leone G et al. 2026
Vitamin C helps the body absorb iron from plant foods and supplements (non-heme iron). Taking them together is a simple way to absorb more.
Calcium can reduce how much iron you absorb, both from food and supplements. Take them at different times of day.
Taking 25 mg iron or more at the same time as zinc can reduce zinc absorption. Take them at different times of day.
Elemental shares for salts are typical values. Most EU and US labels already list the elemental amount, so pick the first option when unsure.
Red meat, liver, legumes, tofu, spinach, fortified cereals (plant iron absorbs better with vitamin C).
Take apart from calcium, zinc, tea, coffee and dairy. Separate from thyroid hormone and some antibiotics.
Iron overdose is dangerous for children: keep bottles locked away. People with haemochromatosis must not take iron.
Pregnant, breastfeeding, on medication, or managing a health condition? Check with a doctor or pharmacist before starting a supplement.
Values checked: November 12, 2026.
Independent summaries to read alongside this page. PillMath is not affiliated with these sites.