Vegan B12 Supplement Dosage Calculator
Vitamin B12 (cobalamin) doesn't occur reliably in plant sources. All B12 on Earth is synthesized by bacteria; animals accumulate it by consuming bacteria-rich foods. Vegans must supplement—it's mandatory—because deficiency causes megaloblastic anemia, peripheral neuropathy, and irreversible neurological damage. The RDA is 2.4 mcg/day, but recommended supplement doses are much higher because absorption drops sharply at higher doses: 250 mcg/day oral or 2000 mcg/week (sublingual or chewable works better than swallowed capsule). For vegan pregnancy and nursing: 250 mcg/day consistently. This calculator provides the correct dose based on your frequency and life stage.
When to use this calculator
- Vegan for >3 months.
- Strict vegetarian without eggs or dairy.
- Vegan pregnancy/nursing.
- Bariatric surgery.
- Age 50+ (reduced natural absorption).
Example: Adult vegan, weekly dosing
- Situation: Adult vegan.
- RDA: 2.4 mcg/day.
- Weekly supplementation: 2000 mcg.
- Form: Cyanocobalamin sublingual.
How it works
1 min readWhat is B12
Water-soluble vitamin synthesized by bacteria.
Why vegans must supplement
Dosing by frequency
| Frequency | Dosage |
|---|---|
| Daily | 250 mcg |
| Twice weekly | 1000 mcg |
| Weekly | 2000 mcg |
Forms
| Form | Advantages |
|---|---|
| Cyanocobalamin | Cheap, stable, most studied |
| Methylcobalamin | Active, better in severe deficiency |
| Hydroxocobalamin | Depot (injectable) |
Signs of deficiency
Diagnosis
Common mistakes
1. Believing spirulina provides B12.
2. Postponing supplement "6 more months".
3. Swallowed capsule (sublingual better for vegans with compromised absorption).
4. Low doses (25 mcg is not enough).
Related calculators
Monitor with bloodwork every 1–2 years.
Frequently asked questions
Is B12 mandatory for vegans?
Yes, always. Swallowed capsule (sublingual better for vegans with compromised absorption).
Does spirulina provide B12?
No. It contains B12 analogues, which are inactive.
What is the daily B12 dosage for vegans?
250 mcg daily or 2000 mcg weekly.
Is sublingual B12 better than capsules?
In some cases yes; capsule works fine if absorption is normal.
Does fortified nutritional yeast count?
Only if fortified and if you're tracking the mcg content.
How often should I test B12 levels?
Serum B12 + methylmalonic acid every 1–2 years. Spirulina and algae contain B12 'analogues' (inactive, can worsen).
What happens without B12 supplementation?
Risk of megaloblastic anemia, neuropathy, and irreversible neurological damage.
Which B12 form is best?
Cyanocobalamin is cheapest and most studied; methylcobalamin is more bioactive.