Vitamin D Calculator
Find out how much vitamin D your body produces from sunlight — and how much you should supplement. Backed by peer-reviewed science.
Click the map or search to set your location. Drag the marker to fine-tune.
☀ Location & Environment
⚫ Personal Factors
Type II: Fair — burns easily, tans minimally
25% of body exposed to sun
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Results will appear here as you adjust the inputs
Scientific Methodology
This calculator combines multiple peer-reviewed models to estimate vitamin D synthesis. Here are the key scientific sources:
UV Index Model
Madronich, S. (2007). Analytic Formula for the Clear-sky UV Index. Photochemistry and Photobiology, 83(6), 1537-1538.
Vitamin D Synthesis
Holick, M.F. (2007). Vitamin D Deficiency. NEJM, 357(3), 266-281.
Skin Type & Melanin
Clemens, T.L. et al. (1982). Increased skin pigment reduces vitamin D3 synthesis. The Lancet, 319(8263), 74-76.
Latitude & Season Effects
Webb, A.R. & Holick, M.F. (1988). Influence of season and latitude on cutaneous synthesis of vitamin D3. JCEM, 67(2), 373-378.
Quantitative Production Rates
Terushkin, V. et al. (2010). Estimated equivalency of vitamin D production from sun vs supplementation. JAAD, 62(6), 929.e1-e9.
Elevation Effect on UV
Blumthaler, M. et al. (1997). Increase in solar UV radiation with altitude. J. Photochem. Photobiol. B, 39(2), 130-134.
Cloud Effects on UV
Calbó, J. et al. (2005). Empirical studies of cloud effects on UV radiation: A review. Reviews of Geophysics, 43(2).
Sunscreen Real-World Efficacy
Faurschou, A. & Wulf, H.C. (2007). The relation between SPF and amount of sunscreen applied. BJD, 156(4), 716-719.
Age-Related Decline
MacLaughlin, J.A. & Holick, M.F. (1985). Aging decreases the capacity of skin to produce vitamin D3. JCI, 76(4), 1536-1538.
Supplementation Guidelines
IOM (2011). Dietary Reference Intakes for Calcium and Vitamin D. National Academies Press. Demay, M.B. et al. (2024). Endocrine Society CPG. JCEM, 109(8).