New to vitamin D? Read the plain-language explainer.
Which places are shown. Only sea-holiday destinations where tourists really go for the beach, diving or islands (for example Spain, Thailand, the Caribbean, Florida), with the United States split into states. Each has its main places, from about 5 for small countries to 20 for big ones, taken from Wikivoyage. Countries without sea-holiday tourism, such as Russia or Germany, stay grey.
How a country is rated. Every main place is rated on its own, and a country takes the rating of its median coastal place: half of its places are better and half are worse. A few good beaches therefore cannot colour a whole country, and if half or more of the places are too hot, too cold or in bad weather, the country is not recommended. The list and the pins show each place’s own rating, and Booking searches go to the country’s best place. Only coastal places (within 30 km of the sea) count; inland places are listed but marked.
When we do not recommend a place. A destination month is marked Too hot when the average afternoon high reaches 34 °C or the “feels like” high reaches 39 °C, and Too cold when the average afternoon high is below 22 °C (too chilly to sunbathe in light clothing). It is marked Bad weather in the rainy or monsoon season (rain on 18 or more days out of 30) and in peak tropical-storm months (hurricanes, typhoons, cyclones). Temperatures and rain are Open-Meteo history for 2023–2024; storm seasons follow NOAA, JMA, Météo-France and BoM.
Method, data sources and notes
How this is calculated. UV comes from the hourly UV Index modelled by Open-Meteo (clouds, ozone and altitude are already included), averaged by month over 2023–2024. Vitamin D counts only when the UV Index is 2.5 or higher. The minutes for a full dose (1000 IU, a quarter of the body bare, no sunscreen) use the Sundi app's burn dose for your skin type and its age line, which cuts vitamin D production by 1.25% for every year over 25 (down to 25%). The rating thresholds are shown in the legend on the map.
Places. The main places per destination are hand-picked: more for big tourism countries such as Spain, Greece, Italy, Thailand, Mexico, Indonesia and Australia, fewer for small ones. Coordinates come from Wikipedia and OpenStreetMap contributors; short descriptions, where shown, from Wikivoyage (CC BY-SA 4.0). Pins are approximate.
Booking links. The Book buttons open a Booking.com search for your dates. They are affiliate links: if you book, Sundi may earn a commission at no extra cost to you. Prices and availability are shown by Booking.com.
Minutes are a rough guide for planning, not medical advice. Burn time is the time to reach one minimal erythemal dose and does not depend on age. Weather, heat, season for crowds and prices are not part of the ranking. For your own day-by-day numbers, use the Sundi app.