According to EatByDate, homemade JELL-O lasts between 7 and 10 days in the refrigerator. JELL-O needs to be stored properly to preserve freshness and flavor. It is best to store JELL-O in an airtight container to avoid cross-contamination from other foods or moisture.
Pre-packaged or already prepared JELL-O should be kept in the refrigerator. Pre-packaged JELL-O lasts for 12 to 18 months in the refrigerator. JELL-O with any signs of mold or watery pockets should be discarded. JELL-O with a bitter taste should also be discarded. JELL-O mixed with fruit or prepared with whipped topping may not last as long as plain JELL-O.