Calculator
Iron: cost per mg of elemental iron
Iron supplements should be compared on elemental iron, the actual iron content: per NHS medicines pages, 210 mg of ferrous fumarate carries about 69 mg of iron, 200 mg of ferrous sulfate about 65 mg, and 300 mg of ferrous gluconate about 35 mg. This calculator converts any product to pence per mg of elemental iron and prices an NHS reference day (14.8 mg for women aged 19 to 49). Ask your GP for a ferritin test before supplementing. Information only, not medical advice.
How the calculation works
We multiply the labelled milligrams by the elemental fraction of the form you select, divide the cost per serving by the elemental milligrams to get pence per mg of iron, and price an NHS reference day at 14.8 mg (women aged 19 to 49; the over-50 figure is 8.7 mg). Many supermarket supplements state elemental iron directly (often 14 mg, 100 percent NRV); for those, choose the elemental option. Fumarate, sulfate and gluconate fractions follow the elemental-iron figures on NHS medicines pages. Bisglycinate varies by product, so treat 20 percent as approximate and check the label.
Reference figures: 14.8 mg and 8.7 mg daily amounts and the 17 mg supplement caution from NHS, Iron; elemental-iron content per form from NHS Medicines A to Z (ferrous fumarate, ferrous sulfate, ferrous gluconate). As of 2026-06-11.
Information only, not medical advice. This tool is educational and is not a substitute for a registered clinician. It does not diagnose anything and does not recommend that you take any supplement. Always read product labels and speak to your GP or pharmacist before starting, stopping or combining supplements. Iron is one to be careful with: ask your GP about a ferritin blood test before supplementing, and keep all iron products away from children, for whom overdose is dangerous.
Read more
See our iron for women guide and the verified figures on our statistics page. More calculators on the cost per effective dose hub.
Frequently asked questions
Why does the iron form change the real dose?
Because the milligrams on the front of the pack are usually the compound, not the iron. NHS medicines pages show that 210 mg of ferrous fumarate contains about 69 mg of iron, 200 mg of ferrous sulfate about 65 mg, and 300 mg of ferrous gluconate only about 35 mg. Two tablets with similar front-of-pack numbers can differ twofold in actual iron.
How much iron do women need a day?
The NHS figure is 14.8 mg a day for women aged 19 to 49, and 8.7 mg a day for women over 50, and most people can get this from food. Needs change with heavy periods, pregnancy and after menopause, which is one reason to talk to your GP rather than guess.
Should I take an iron supplement without a blood test?
It is wiser not to. Tiredness has many causes, iron overload is possible, and the NHS notes that side effects like constipation and stomach upset are common at higher doses. Ask your GP about a ferritin blood test before supplementing; if you are deficient, your GP can prescribe the right dose.
Is there a safe upper amount for iron supplements?
The NHS states that taking 17 mg or less a day of iron supplements is unlikely to cause harm, and that higher doses should be taken only under medical advice. The calculator flags servings above that figure. Prescribed treatment doses for diagnosed deficiency are a different matter and belong with your prescriber.
Editor, Her Vitals
Oliver leads Her Vitals's editorial coverage of women's life-stage health and supplements. He curates and reviews existing branded products across trying to conceive, pregnancy, postnatal, perimenopause, menopause and the senior years, weighing what the evidence supports against guidance from bodies such as EFSA, the NHS and NICE, and is clear that the content is information rather than medical advice.
Last reviewed: 11 June 2026