After opening a bottle of spaghetti sauce, it is generally recommended to store it in the refrigerator and use it within 3 to 5 days. This timeframe ensures the sauce remains safe to eat and maintains its quality. Always check the label on the bottle for any specific storage instructions or "use-by" dates provided by the manufacturer.
If you can't consume the entire bottle within that time frame, consider transferring the leftover sauce into an airtight container before refrigerating. This can help prolong its freshness and prevent any potential contamination. If you don't think you'll use the sauce within a few days, you can also freeze it for longer storage. When properly frozen, spaghetti sauce can typically last for several months.