A bottle of Champagne remains drinkable for a few days, with the exact number depending on storage conditions and whether or not you plug the bottle's opening.
Temperature also greatly affects how long Champagne retains its signature effervescence. The colder you keep your bottle, the better it will retain its fizz.
Proper storage in a cold fridge will keep the wine drinkable for up to five days in the best-case scenario. Poorly preserved Champagne can go flat in as little as two days.
A good bottle stopper and a very cold refrigerator work in tandem to keep the drink fresh and bubbly for as long as five days.
Size is another factor in how well Champagne is preserved. An unopened 3-liter Jeroboam of Champagne has more than triple the shelf life of a normal-sized 750-milliliter bottle.