Sun Day
Enjoy the sun without worry. Sun Day measures your real-time UV index based on your exact location, tracks your Vitamin D synthesis and alerts you at the right moment to protect your skin.
Sun exposure, mastered
Sun Day combines accurate environmental data with personal health tracking so you can confidently enjoy the outdoors.
Real-time UV Index
Precise data based on your exact location, continuously updated for at-a-glance decisions.
Vitamin D Tracking
Personalized synthesis estimate based on your skin type, clothing and exposure time.
Smart Alerts
Sun Day notifies you when it's time to seek shade or reapply sunscreen — never spam, only what matters.
Trusted Data
Powered by Open-Meteo, an open and reliable source used by professional weather services.
Total Privacy
No ads, no tracking. Your health data stays on your device. Always.
Hourly Forecast
Plan your outings with hourly UV forecasts and the optimal exposure window for the day.
Your sun health, simplified
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Personalized for your skin
Vitamin D calculation adapts to your phototype (I to VI) and clothing habits.
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Contextual alerts
Discreet notifications only when your skin is at risk — never every five minutes.
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Moon phase & sunrise
As a bonus, follow the moon phase, sunrise and sunset times to plan your day.
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Crafted by DIH LABS
Built by our non-profit association dedicated to useful, ethical, ad-free digital tools.
Sun safety resources
Learn more about UV index, vitamin D and sun protection.
Best Free UV Index App
Why tracking UV in real time has become essential in 2026.
Best Weather App with UV Index
When a weather app is enough and when a dedicated UV tracker is better.
Vitamin D & Sun: The Complete Guide
How many minutes of sun you actually need, by skin type.
Free Vitamin D Tracker
Track sun exposure, UV index and vitamin D estimation without ads.
Sun Protection & SPF
Understand SPF ratings and pick the right sunscreen.
Sunscreen for Dark Skin (Fitzpatrick IV–VI): The Honest Guide
Why darker skin still needs SPF, how to avoid the white cast, what filters actually work, and why hyperpigmentation is t…
Tanning vs Sunburn: The Science Behind Why "A Base Tan" Is a Myth
The melanin pathway, immediate vs delayed pigmentation, MED, and why every tan is DNA damage.
How a UV Application Actually Works in 2026 (Sensors, Models, Accuracy)
What's really inside a UV application?
UV Index and Skin Types: The Fitzpatrick Scale
Learn how your skin type reacts to the UV Index.
UV Index by Month: A Year-Round Calendar for Every Latitude
What UV index to expect each month, from January to December, depending on your latitude.
UV Index in Winter: Why You Still Need Protection
Don't let the cold fool you.
UV Index on Cloudy Days: Why You Still Burn Under the Clouds
Cloud cover blocks light, not UV.
UV Protection for Children: A Parent's Guide (0–12 years)
A pediatric-grade guide to protecting children from UV.
UV Protection for Your Eyes: Cataracts, Photokeratitis & the Sunglasses That Work
Why your eyes burn before your skin does, what UV does inside the eye over decades, how to choose sunglasses that actual…
Vitamin D Deficiency: Symptoms, Tests & What to Do About It
The real signs of low vitamin D, the only blood test that matters, target ranges, and how much sun or supplementation ac…
Vitamin D Dosage Calculator: Sun, Supplements, and How Much You Really Need
How many IU of vitamin D you actually need by age, weight, skin type and latitude — and what the sun can realistically g…
Enjoy the sun, with confidence.
Download Sun Day for free and take back control of your sun exposure.