
RayDay: Vitamin D Tracker
Your Daily Sunlight Window
About
This app calculates your daily window for natural Vitamin D production based on your location and skin type. It provides solar path visualization, forecasts, and atmospheric data to help you optimize sun exposure safely.
What's New in RayDay
1.4.1
October 17, 2026
Built for the bigger screen. On iPad and on the iPhone Duo's inner display, RayDay now lays out in two columns instead of one stretched one. The solar arc, your conditions and the session button sit on the left. Today's total, the week ahead and your latest badge sit on the right. • Two columns on Today, History and sun sessions wherever there is room • Your Year shows up to four months at a time on a large iPad • Cards no longer stretch across the width of a 13-inch screen • The sun session screen now lays out differently in portrait and in landscape
MoreSubscriptions & In-App Purchases
RayDay Yearly
A full year of D-Window, IU tracking & forecasts.
Developer apps
FAQ
What is RayDay's D-Window?
RayDay's D-Window is the period each day when the sun's altitude is above 35° and UVB rays can penetrate the atmosphere for Vitamin D synthesis. The app calculates this window based on your location and skin type.
How does RayDay personalize sun exposure?
RayDay uses your Fitzpatrick skin type to recommend exposure durations. This helps you achieve your daily Vitamin D IU goal without risking overexposure.
Does RayDay work worldwide?
Yes, RayDay is designed to be accurate for any latitude, including polar regions. It uses NOAA solar position algorithms for precise calculations.
What atmospheric data does RayDay provide?
The app offers real-time UV index, cloud cover, humidity, and altitude. This information helps you understand current conditions affecting sun exposure.
Can I get alerts from RayDay?
Yes, RayDay offers smart notifications. You'll receive alerts before optimal sun days and a reminder when winter's first D-Window returns.
What is RayDay's rating and update frequency?
RayDay has a rating of 3.0 stars from 2 ratings. The app was last updated on June 24, 2026, indicating recent development activity.
Is RayDay available on all devices?
RayDay is supported on iPhone and iPad devices. It is rated for ages 4 and up.
Does RayDay have ads?
No, RayDay is ad-free. It is a free application with no advertisements to interrupt your experience.






