Iron Dosage Calculator
The oxygen-transport mineral. Essential for haemoglobin, myoglobin, and mitochondrial energy production. The world's most common nutritional deficiency — but supplementation without confirmed deficiency is dangerous.
What is Iron?
Iron (Fe) is an essential trace mineral and the central atom of haemoglobin (which carries oxygen in red blood cells), myoglobin (oxygen storage in muscle), and the cytochrome electron transport chain enzymes critical for mitochondrial ATP synthesis. Iron deficiency is the most prevalent nutritional deficiency worldwide, affecting approximately 2 billion people, with iron deficiency anaemia (IDA) the endpoint of a continuum that begins with depleted iron stores (low ferritin) progressing through functional deficiency (elevated transferrin, low serum iron) before culminating in anaemia (low haemoglobin). Symptoms at earlier stages (without frank anaemia) include fatigue, brain fog, impaired exercise performance, restless leg syndrome, and hair loss. High-risk groups: premenopausal women (menstrual losses), pregnant women, endurance athletes (foot-strike haemolysis, GI microbleeds, sweat losses), infants, and strict vegans/vegetarians (non-haem iron from plants has 2–15% absorption versus 20–35% for haem iron from meat). Iron supplementation should only be initiated after laboratory confirmation of deficiency (serum ferritin, serum iron, TIBC, haemoglobin). Supplementing in iron-replete individuals does not improve energy or performance and carries real toxicity risk.
How to Take Iron
Iron supplementation doses depend on the severity and indication. **Iron deficiency without anaemia (low ferritin, normal Hb):** 15–30 mg elemental iron/day. **Iron deficiency anaemia:** 100–200 mg elemental iron/day in divided doses, under physician supervision. **Prophylactic (pregnancy, heavy periods):** 27–60 mg/day (per obstetric guidelines). Form matters significantly: ferrous bisglycinate chelate (e.g., Ferrochel) has 2–4× higher bioavailability and 75% lower GI side effects compared to ferrous sulfate — the historical standard that is still common but poorly tolerated. Ferrous gluconate and ferrous fumarate are intermediate options. Avoid ferric iron (Fe³⁺) forms (ferric orthophosphate) — substantially lower bioavailability.
Timing Recommendations
Taking iron on an empty stomach maximises absorption (gastric acid enhances Fe³⁺ → Fe²⁺ reduction and ferritin solubility), but is poorly tolerated due to severe GI discomfort. The compromise: take iron with a small vitamin C-rich food or drink (orange juice, 100 mg vitamin C supplement) — ascorbic acid reduces ferric to ferrous iron and chelates it in a soluble complex, enhancing absorption by 2–3× and mitigating GI side effects. Critically, never take iron with coffee, tea (tannins), dairy (calcium), eggs (phosvitin), or calcium supplements — all potently inhibit non-haem iron absorption. Alternate-day dosing (every other day) has been validated in multiple RCTs to be equally effective as daily dosing for IDA correction, with significantly fewer GI side effects and better compliance, likely because it avoids the hepcidin spike that daily supplementation triggers.
Potential Side Effects & Safety
GI side effects are universal with oral iron: constipation, dark/black stools (harmless), nausea, and abdominal cramping — all dose-dependent and form-dependent. Ferrous sulfate at 200 mg/day produces GI adverse effects in 30–40% of patients; ferrous bisglycinate at equivalent elemental doses shows < 10% GI complaint rates. Iron overload (haemochromatosis) is potentially lethal, presenting as liver cirrhosis, cardiomyopathy, pancreatic damage (diabetes), and joint arthropathy — do not supplement without confirmed deficiency. Accidental iron overdose is a leading cause of death by poisoning in children under 6 — store iron supplements in childproof containers.
Who should avoid Iron?
**Hereditary haemochromatosis (HFE gene mutation):** Absolute contraindication — these individuals hyper-absorb dietary and supplemental iron and accumulate toxic levels in organs. **Thalassaemia and haemolytic anaemias:** Iron does not treat these conditions and supplementation is harmful. **No laboratory-confirmed deficiency:** Iron supplementation in iron-replete individuals is not beneficial, may cause GI harm, and generates oxidative stress (free iron catalyses the Fenton reaction, producing hydroxyl radicals). Men and post-menopausal women should confirm low ferritin before supplementing. Drug interactions: iron reduces absorption of levodopa, levothyroxine, quinolone antibiotics, and bisphosphonates.
Best Stacks with Iron
Vitamin C (250–500 mg taken simultaneously) is the most important iron co-factor — enhances absorption 2–3× and reduces GI side effects. For pregnant women, iron + folic acid (400–800 mcg) addresses the two most common deficiencies of pregnancy simultaneously. Avoid stacking with calcium, zinc, or magnesium at the same dose — all compete for divalent metal transporters and reduce iron absorption.
Scientific References
All dosage recommendations are grounded in peer-reviewed research.
- 1
- 2Alternate-day versus consecutive-day oral iron supplementation in patients with iron-deficiency anaemia
The Lancet Haematology · 2017
Iron Dosage Calculator
Fixed dosage — independent of body weight
Your recommended daily dosage
Formula: 15–30 mg/day (mild deficiency) | 100–200 mg/day (IDA, physician-supervised) — confirm deficiency before supplementing
Safety notes
- DO NOT supplement without a blood test confirming iron deficiency (serum ferritin, Hb) — iron supplementation in iron-replete individuals is harmful.
- Keep iron supplements locked away from children — iron overdose is a leading cause of paediatric poisoning death.
- Take with vitamin C (250 mg) to improve absorption and reduce GI side effects. Avoid coffee, tea, dairy, or calcium within 2 hours of dosing.
- Alternate-day dosing is as effective as daily dosing for IDA with significantly fewer GI side effects.
- Hereditary haemochromatosis (HFE gene mutation): iron supplementation is absolutely contraindicated.
- Separate iron from thyroid medication (levothyroxine), levodopa, and antibiotics by at least 2 hours.
This calculator provides general guidance only. Always consult a qualified healthcare professional before starting any supplement.