Unopened soda bottles retain their carbonation the longest, exceeding the printed sell-by date on their labels. When stored under optimal conditions, unopened bottles of soda can stay fizzy for up to nine months beyond this marked date. For a long shelf life, store plastic bottles of soda in a cool location with a constant temperature and without direct sunlight exposure. While soda won't typically be spoiled beyond the expiration date, it is likely to be noticeably flat after nine months of pantry storage beyond the sell-by date even under optimal conditions.

Once opened, the shelf life of a bottle of soda is relatively short at just three to five days. Storage in a pantry once opened gives you at most three days of carbonation, while refrigerated some sodas remain carbonated for up to five days. Store soda in its original bottle and ensure that you tightly close the top to get the longest shelf life once the bottle has been opened. Carbonation dissipates gradually as the days go by, so drink opened soda sooner rather than later when possible.

While the carbonation in diet sodas doesn't dissipate any quicker, saving diet sodas beyond the recommended nine months can yield an unpalatable glass of soda. Artificial sweeteners break down over time and impart a bad taste, making it important to drink these products closer to the sell-by date for the best taste as well as good carbonation. While it's still safe to drink diet soda up to nine months after its sell-by date, if your diet soda has an undesirable taste, discard it.

Carbon dioxide eventually escapes from an unopened bottle of soda and this is unpreventable. However, you can prevent the unnecessarily short life of an opened bottle of soda by using some convenient gadgets to aid in keeping it carbonated. Carbonation pumps are an at-home solution for re-carbonating drinks, while several gadgets that allow you store soda bottles upside down can help stop the quick loss of carbon dioxide gas before your soda is finished. Without using fancy gadgets, you can extend the shelf life of opened soda bottles by tightly placing the cap on the soda after use and not allowing the bottle to stand uncapped for longer than the time it takes to pour your drink.