Calculate your personalized vitamin D supplementation dose based on your current level, target level, and body weight using the simplified Heaney formula.
An estimated 42% of U.S. adults are vitamin D deficient (<20 ng/mL), and over 70% are below the optimal range. Modern indoor lifestyles, sunscreen use, living at higher latitudes, and darker skin tones all reduce vitamin D production. Unlike most vitamins, vitamin D is difficult to get from food alone — sunlight exposure and supplementation are the primary sources.
Why it matters: Vitamin D is not just a vitamin — it functions as a hormone that affects over 200 genes. Deficiency is linked to weakened immunity, bone loss, depression, fatigue, muscle weakness, and increased risk of autoimmune disease, cardiovascular disease, and certain cancers.
After starting supplementation, retest your 25-hydroxyvitamin D level in 8-12 weeks. It takes about 2-3 months for levels to stabilize at a new steady state. Once you reach your target, test every 6-12 months to ensure your maintenance dose is adequate — levels can drop in winter months.
Pro tip: Take vitamin D3 (cholecalciferol, not D2) with a fat-containing meal for best absorption. Adding vitamin K2 (MK-7) helps direct calcium to bones rather than arteries.
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Upload lab results, track your vitamin D over time, and let AI tell you when to retest. See how supplementation, sun exposure, and seasonal changes affect your levels.
Start Tracking FreeThis calculator is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider before starting supplementation. High-dose vitamin D can cause toxicity — do not exceed recommended doses without medical supervision.