Unopened detergent can typically last up to two years, depending on the type. However, it is recommended to check the expiration date on the packaging to be sure. After opening the package, it is best to use the detergent within six months, as it will start to lose its potency after that time. It is also important to store the detergent in a cool, dry place, away from direct sunlight. If these conditions are not met, the detergent may not last as long.