Vitamin D depends on many factors: season, latitude, weather, time of day, skin type, clothing, age, sunscreen and time outdoors. A free vitamin D tracker app like Sun Day does not claim to know your blood level. It makes visible what most weather apps treat as an afterthought: the connection between UV index, exposure and daily estimation.
Why track vitamin D and UV together?
The same sunlight can be useful or harmful depending on context. When the UV index is too low, vitamin D synthesis may be limited. When it is high, sunburn risk rises quickly. Sun Day brings both signals together so you can decide whether to enjoy the sun, wait, protect your skin or seek shade.
What Sun Day takes into account
| Signal | Role in Sun Day |
|---|---|
| Local UV index | Core sun-exposure signal |
| Skin type | Adapts sensitivity to sunlight |
| Exposure duration | Tracks your daily accumulation |
| Protection and clothing | Refines exposed-skin estimation |
| Alerts | Warns when risk increases |
Free and ad-free
Personal health topics deserve a calm interface. Sun Day was built by DIH LABS as a free app with no advertising: no banners inside your data, no interruption when you check the UV index, and no constant pressure toward a subscription.
Who is Sun Day useful for?
- People who want to understand daily sun exposure.
- Outdoor athletes who train around midday.
- Parents watching children's sun exposure.
- Users looking for a cleaner alternative to ad-heavy weather apps.
Related guides
Continue with our vitamin D and sun guide, the vitamin D dosage calculator and the guide to UV index and skin types.
Download Sun Day
The free, ad-free UV and vitamin D app.