Calculators
Cost per effective dose calculators
Supplement prices only make sense per effective dose of the active ingredient: per 10 micrograms of vitamin D, per 100 mg of elemental magnesium, per gram of EPA plus DHA, per 10 g of collagen, per milligram of elemental iron. These free calculators do that conversion instantly from any UK label, using NHS and EFSA reference figures. Information only, not medical advice.
Vitamin D
Headline number: pence per 10 mcg (400 IU), the NHS reference amount.
Accepts mcg or IU. Flags servings above the NHS 100 mcg daily guidance.
Magnesium (form-adjusted)
Headline number: pence per 100 mg of elemental magnesium.
Adjusts for glycinate, citrate, oxide and more; "500 mg glycinate" is about 70 mg of magnesium.
Omega-3
Headline number: pounds per gram of combined EPA + DHA.
The number "1000 mg fish oil" labels hide. Works for fish and algae oils.
Collagen
Headline number: pence per 10 g hydrolysed-collagen serving.
Shows why capsules are often 10x dearer than powder, and that 0 EFSA claims are authorised.
Iron (form-adjusted)
Headline number: pence per mg of elemental iron.
Uses the NHS elemental figures for fumarate, sulfate and gluconate. Ferritin-test caveat included.
How we built these
Every reference figure is taken from a named primary source (NHS reference intakes and cautions, the EFSA-authorised claims register) and dated, and every conversion is shown on the tool page. Mineral form fractions come from molecular weights and NHS medicines pages. The calculators run entirely in your browser; nothing you type is sent anywhere, and there is no sign-up.
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.
Read more
Our guides cover the evidence behind each category: vitamin D, magnesium, omega-3, collagen and iron for women. For live NHS data, see the UK HRT Prescribing Tracker.
Frequently asked questions
What does cost per effective dose mean?
It is the price of the amount of active ingredient a reference body actually talks about, such as 10 micrograms of vitamin D (NHS) or 250 mg of EPA and DHA (the EFSA-authorised claim), rather than the price per pack or capsule. It is the only number that compares products fairly across pack sizes, strengths and forms.
Why do these calculators adjust for the form?
Because for minerals the label weight is mostly not the mineral. Magnesium glycinate is about 14 percent magnesium and ferrous gluconate about 12 percent iron, so the front-of-pack milligrams overstate what you get. The magnesium and iron calculators convert to elemental amounts before pricing.
Do the results tell me which supplement to take?
No. They tell you what each product honestly costs, nothing more. Whether you need a supplement at all depends on your diet, life stage and health, which is a conversation for your GP or pharmacist; the NHS advises most nutrients are best obtained from food.
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