The Whisky.com team estimates the shelf life of an opened bottle of whiskey to be between six months and two years. The Scotch Whisky Association says it can last indefinitely with proper storage.
If the opened bottle of whiskey is kept upright in cool, dry conditions and out of direct sunlight, and the cork or cap is secured on top, whiskey can last for a long time. As time goes by, the whiskey may react to the air in the bottle. Evaporation may also occur. These elements can cause minute changes to the flavor of the whiskey. However, as long as the whiskey is not otherwise contaminated, it is still safe to drink.