Officially, the shelf life of dark chocolate is two years. Unofficially, it should last much longer than that - there are documented reports of dark chocolate still being edible after 100 years of storage. As part of our own experiment, we have chocolate bars that have been stored in our office for up to six years, and they are still in excellent condition. But we don’t recommend trying that at home. Why wait?
Dark chocolate likes to be stored within the temperature range of 12-22° C (53-72° F). Temperatures as high as 25° C (77° F) are usually fine. The official melting point of dark chocolate is around 30° C (86° F).
From a health and safety perspective, it will still be viable to eat for several years. From a flavor and aroma perspective, it’s best to eat it within a week or so of opening the bar. If you do want to preserve a bar after opening, store it in a ziplock bag. This can help maintain flavors and aromas for months.