First of all, there are big differences between the various butterfly species. As discussed in the article types of butterflies, there are more than 18,000 species of butterflies.
The climate also affects the length of their lives. Although there are butterflies that survive the winter, most of them die when the temperature drops. Usually, butterflies hibernate as an egg, a caterpillar or a pupa. These are the other life stages discussed in the butterfly life cycle. As an egg or caterpillar, they are much better protected against the cold temperatures. Another possibility is that the butterflies migrate to the south. Finally, I would also cite that a lot of butterflies die because they are a victim of predators.
As you can see, there is no simple answer to the question how long butterflies live, but in general we can assume that an adult butterfly can live for a month. If you add the other stages of the butterfly life cycle (egg, caterpillar, pupa), they can survive up to a year.