Most adults with iron deficiency anemia are prescribed 100 to 200 mg of elemental iron per day, though recent evidence suggests that lower doses taken every other day may work just as well with far fewer side effects. The right amount for you depends on how severe your anemia is, your age, and whether you’re pregnant, but understanding elemental iron (the actual iron your body can use) versus the total milligrams on the bottle is the first step to getting this right.
Elemental Iron vs. What’s on the Label
This is where most people get confused. Iron supplements list the total weight of the iron compound on the label, but only a fraction of that is actual, usable iron. A standard 325 mg tablet of ferrous sulfate contains only about 65 mg of elemental iron. Ferrous fumarate packs more iron per pill (about 99 mg of elemental iron in a 300 mg tablet), while ferrous gluconate delivers the least (roughly 39 mg per 325 mg tablet).
When your doctor says “take 60 mg of iron twice a day,” they mean 60 mg of elemental iron, not 60 mg of whatever salt form you bought. Always check the supplement facts panel for “elemental iron” to make sure you’re hitting the right number.
Standard Adult Dosage
For mild to moderate iron deficiency anemia, a common starting point is 60 to 120 mg of elemental iron per day. More severe cases sometimes call for up to 200 mg daily, split into two or three doses. These amounts exceed the tolerable upper intake level of 45 mg per day set by the National Institutes of Health for healthy adults, but that threshold is designed for people without a deficiency. Doctors routinely prescribe higher doses when iron stores need replenishing.
In practice, this often looks like one or two tablets of ferrous sulfate (325 mg each, providing about 65 mg elemental iron per tablet) taken throughout the day.
Every Other Day May Be Better
Your body has a built-in regulator called hepcidin, a hormone that rises after you take iron and temporarily blocks further absorption. Taking iron every day keeps hepcidin elevated, which means a good portion of your second or third daily dose passes straight through your gut unused, often causing stomach problems along the way.
A randomized trial found that taking 60 mg of elemental iron on alternate days for 28 days produced better absorption than the same total amount given daily over 14 days. A 2024 trial in India drove the point home even further: women taking 120 mg of elemental iron every other day saw greater hemoglobin increases than those taking 60 mg daily, and only 9% experienced gut side effects compared to 45% in the daily group. A Swiss trial confirmed similar ferritin improvements with fewer side effects and lower rates of recurring deficiency over six months.
A 2025 systematic review and meta-analysis concluded that alternate-day dosing is comparably effective to daily dosing for mild to moderate anemia, with better tolerability. That tolerability matters because people who feel terrible on iron supplements often stop taking them, which defeats the purpose entirely.
During Pregnancy
Pregnant women need significantly more iron. The WHO has studied supplementation doses ranging widely, but most prenatal guidelines recommend 30 to 60 mg of elemental iron daily for prevention and higher amounts if anemia is already present. The tolerable upper limit remains 45 mg during pregnancy, but as with non-pregnant adults, doctors prescribe above that threshold when iron stores are low. Prenatal vitamins typically contain 27 to 30 mg of elemental iron, which is enough for prevention but usually not enough to treat established anemia.
Dosing for Infants and Children
Children’s doses are weight-based. For treating iron deficiency anemia, the standard range is 3 to 6 mg of elemental iron per kilogram of body weight per day, split into two or three doses. Lower doses (around 3 mg/kg) are used for mild anemia, while more severe cases warrant the higher end. For prevention in breastfed infants, the American Academy of Pediatrics recommends 1 mg/kg per day starting at four months. Preterm infants typically start earlier, at about 2 mg/kg per day beginning around one month of age, continuing through 12 months.
How Long Treatment Takes
You won’t feel better overnight. In a randomized clinical trial, people taking iron supplements saw hemoglobin begin recovering in about 30 to 32 days. Full hemoglobin recovery, reaching levels slightly above baseline, plateaued around 120 days (about four months) of consistent supplementation.
Replenishing your iron stores (measured by ferritin) takes even longer and varies depending on how depleted you were at the start. People who began with very low ferritin recovered their baseline levels in a median of 21 days with supplements, but reaching a healthy ferritin level of 26 ng/mL or higher took a median of 120 days. Those who started with higher (but still insufficient) ferritin took about 107 days to recover baseline levels. Without supplements, more than two-thirds of people in the trial hadn’t recovered their ferritin even after 168 days.
The takeaway: plan on at least three to six months of supplementation, and don’t stop just because you feel better. Your hemoglobin may normalize well before your iron stores are fully replenished.
What Helps Absorption
Iron is best absorbed on an empty stomach, ideally 30 to 60 minutes before eating. Vitamin C taken at the same time dramatically improves uptake. The effect is dose-dependent: in one study, increasing vitamin C from 25 mg to 1,000 mg boosted iron absorption from 0.8% to 7.1%. Even a modest glass of orange juice (around 70 to 80 mg of vitamin C) makes a meaningful difference. The key is that both nutrients need to be consumed together. Taking vitamin C four to eight hours before iron provides little benefit.
Calcium works against you. It reduces iron absorption by 18 to 27%, so separate calcium supplements or dairy-heavy meals from your iron dose by at least two hours. Coffee and tea contain compounds that also inhibit absorption, so keep those away from your iron window as well.
Managing Side Effects
Stomach cramps, nausea, constipation, and a metallic taste are the most common complaints. If you’re taking iron on an empty stomach and it’s making you miserable, taking it with a small amount of food is a reasonable trade-off. You’ll absorb slightly less, but you’ll actually keep taking it.
A few practical strategies that help:
- Switch to alternate-day dosing. This is the single most effective change for reducing gut symptoms, backed by multiple trials.
- Try a lower-iron formulation. Ferrous gluconate delivers about 39 mg of elemental iron per tablet versus 65 mg for ferrous sulfate, which can be gentler on the stomach.
- Start low and build up. Taking a smaller dose for the first week gives your gut time to adjust before increasing.
- Use a stool softener. If constipation is the main problem, an over-the-counter stool softener like docusate sodium can help while your body adjusts.
- Ask about switching forms. If one type of iron salt is intolerable, a different form may sit better. Don’t just stop taking iron without exploring alternatives.
Nausea tends to be worse at higher doses. Splitting your daily amount into smaller portions taken at different times can reduce it, though if you’re using alternate-day dosing, you’re already concentrating your intake. In that case, taking the dose with a small snack and vitamin C is a good compromise.