How this works. Vitamin D time uses the maintenance-dose method from Kift & Webb (2024),
Nutrients 16:1489 — the short, sub-burn exposure that keeps your vitamin D topped up, scaled by skin type (types V and VI need 2.5× and 4× longer) and the live UV index. Cooked time estimates sunburn from your skin's minimal erythemal dose and the current UV. This is a friendly guide, not medical advice.
Where the UV comes from. Live readings come from the
Open-Meteo Forecast API, whose
uv_index is derived from NOAA's GFS model and updates every six hours. It's the erythemal (sunburn-weighted) UV index on the standard WHO 0–11+ scale, and it accounts for real cloud cover and ozone. If that feed can't be reached, the page falls back to a model computed in your browser: solar geometry for the sun's angle, the van Heuklon (1979) ozone climatology for absorption, and a background turbidity factor. Checked against NOAA/EPA's published city forecasts it lands within about a point.