Vitamin B12 Dosage Calculator
Calculate your personalised vitamin b12 dose based on Australian guidelines. NHMRC RDI: 2.4 mcg/day (male) / 2.4 mcg/day (female).
Calculate Your Dose
Important Warnings
- Strict vegans must supplement — there are no reliable plant sources of B12.
- Metformin (diabetes medication) reduces B12 absorption — test levels regularly.
- High B12 blood levels without supplementation can indicate liver disease — see a doctor.
- Intrinsic factor deficiency (pernicious anaemia) requires injections or very high oral doses.
Tips for Better Absorption
- Sublingual (under the tongue) tablets may improve absorption for those with gut issues.
- Oral B12 works even for pernicious anaemia at doses above 1,000 mcg.
- Don't rely on spirulina or nutritional yeast as your only B12 source.
- Get tested annually if you're vegan, over 50, or on metformin.
Frequently Asked Questions
Do vegans need B12 supplements?
Yes, absolutely. There are no reliable plant sources of vitamin B12. All major health organisations recommend vegans take 250–500 mcg daily or 2,500 mcg weekly. B12 deficiency can cause irreversible nerve damage.
Is methylcobalamin better than cyanocobalamin?
Both are effective. Methylcobalamin is the active form (no conversion needed). Cyanocobalamin is more studied and cheaper. For most people, either works well. Choose methylcobalamin if budget allows.
Can you take too much B12?
No upper limit has been established. B12 is water-soluble — excess is excreted in urine. Studies using doses 1,000x the RDI found no toxicity. Supplements commonly contain 500–5,000 mcg, all considered safe.
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This calculator provides general guidance based on Australian NHMRC guidelines and published clinical research. It is not medical advice. Individual needs vary. Always consult a healthcare professional before starting any supplement, especially if you are pregnant, breastfeeding, taking medications, or have a medical condition.