How long does martini last when open?

An opened bottle of vermouth, the primary ingredient in a martini, typically lasts about 1 to 3 months when stored in the refrigerator. The gin or vodka used in a martini doesn't spoil, but its flavor may change over time. For the best taste, it's recommended to consume the martini soon after it's made. Always check for any off odors or changes in flavor before drinking.