Iron Dosage Guide (2026): How Much Iron Per Day by Age & Sex

By Erin Rose · Published July 10, 2026 · Updated August 28, 2026 · Methodology

Summarizes NIH guidance and published clinical research — not medical advice. Iron supplementation should be guided by a blood test and a clinician.

Know your dose? See the best iron picks at that dose →

As an Amazon Associate we earn from qualifying purchases. Picks are ranked by tolerability, cost per dose, and certification — never commissions.

Recommended Daily Allowance (RDA)

These are the total daily iron needs from all sources (food + supplements), set by the National Institutes of Health:

Source: NIH Office of Dietary Supplements. Vegetarians and vegans are advised to aim ~1.8× higher, because non-heme (plant) iron is absorbed less efficiently. The Tolerable Upper Intake Level is 45mg/day for adults.

Elemental iron vs. tablet strength

This trips up almost everyone. An iron tablet is only partly iron — the rest is the salt it's bound to. "Elemental iron" is the amount your body actually gets, and it's the number that matters for dosing. A "325mg" ferrous sulfate tablet is really about 65mg of elemental iron.

How to read the label: look at the Supplement Facts panel for the "Iron" line and its milligram amount — that's the elemental iron. Bisglycinate products typically state the elemental amount directly (e.g., 25mg), which is one reason they're easy to dose.

Where this trap actually lives. We went looking for it across the market and mostly did not find it: of the 178 labels that print a milligram figure in the product name and declare iron on the panel, 95% agree within 15%. The reason is that “325 mg ferrous sulfate” is a pharmacy convention — it is how a prescription or behind-the-counter strength is written, and it names the salt. Supplement brands label their own bottles, and they overwhelmingly print the elemental figure on the front. So the conversion table above is the one you need when a clinician or a pharmacist hands you a number, and the panel is the one you read on a shelf. Check the panel either way — but do not assume the number on a supplement bottle is inflated.

The modern approach: alternate-day dosing

If you're treating a confirmed deficiency, the old advice — a large dose two or three times a day — turns out to be partly self-defeating. A big iron dose spikes hepcidin, the hormone that shuts down iron absorption for roughly a day, so dosing more often doesn't proportionally help and just adds side effects. Research found that a single dose every other day raised the fraction absorbed and reduced GI upset (Stoffel 2017, PMID: 29032957; Kamath 2024, PMID: 37979057). The AGA's clinical update on iron deficiency reflects this shift toward lower-frequency dosing (DeLoughery 2024, PMID: 38864796). Practically, many people do well on ~60–100mg of elemental iron every other day with vitamin C — but let your doctor set the target based on how depleted you are. See iron for anemia & low ferritin for the full treatment picture.

How to absorb iron better

• Pair it with vitamin C. Take iron with a citrus fruit, a glass of orange juice, or a vitamin C supplement — it meaningfully increases absorption of non-heme iron.
• Empty-ish stomach, if you tolerate it. Food lowers absorption, but if iron upsets your stomach, taking it with a little food is a fair trade for staying consistent.
• Separate from blockers. Keep iron a couple of hours away from calcium supplements, dairy, coffee, and tea — all blunt absorption.
• Choose a tolerable form. You'll be taking it for months, so tolerability wins. Ferrous bisglycinate causes less constipation and nausea than ferrous sulfate. See ferrous sulfate vs bisglycinate.
• Be patient. Hemoglobin recovers in weeks, but ferritin — your storage tank — takes 3–6 months to refill. Recheck ferritin, not just hemoglobin, before stopping. See how long iron takes to work for the two timelines side by side.

What "low" actually means on a blood test

This guide keeps telling you to test before supplementing, so it owes you the threshold. The number that matters is ferritin, which measures stored iron — not haemoglobin, which measures the iron currently in circulation. Stores empty first. You can be genuinely iron deficient with a completely normal blood count, and a standard CBC will not show it.

A systematic review of this state — non-anaemic iron deficiency — defined it as ferritin below 16 µg/L with no anaemia (below 12 in children under five) (Pratt 2016, PMID: 26256281). That is the group most likely to be told their bloods are “fine” while feeling anything but. If you are tired and your haemoglobin came back normal, ferritin is the test to ask for by name.

Restless legs is the other reason people are sent to the iron aisle without anaemia. Iron supplementation for restless legs syndrome has been pooled across randomised trials (Avni 2019, PMID: 30798983), and it is one of the few cases where treating on a ferritin result rather than a haemoglobin result is standard practice. It is still a result, not a symptom — get the number first.

Pregnancy is not an exemption from testing, even though routine iron is normal there. A systematic review of daily iron in pregnant women who were neither anaemic nor iron deficient found the benefits and harms unclear (Hansen 2023, PMID: 37403900). Prenatal care usually checks iron status anyway — the point is that “pregnant” is not by itself the indication, the blood test is.

When you should not take iron

Iron is genuinely one to be careful with. Skip supplemental iron unless a test says otherwise if:

• You have no confirmed deficiency — a normal or high ferritin means you don't need it, and extra iron isn't a wellness booster.
• You have hemochromatosis or another iron-overload condition.
• You've had unexplained iron deficiency without finding the cause — deficiency in men and post-menopausal women especially can signal bleeding that needs investigation first.

The safe rule: a ferritin test is cheap, iron overload is not reversible on your own, and "just in case" iron does more harm than good.

Frequently asked questions

Related guides

• Iron for Anemia & Low Ferritin — dose, duration, and absorption for a confirmed deficiency
• Ferrous Sulfate vs Bisglycinate — the tolerability difference that matters over months
• Iron for Women — menstruation, pregnancy, and higher needs
• How Long Does Iron Take to Work? — hemoglobin vs ferritin timelines
• Best Iron Supplements — products ranked by cost per dose
• All Iron Products

Sources