Most sealant manufacturers will have their own recommendations for how long their sealant lasts and how often it should be refreshed or replaced. It can vary depending on what climate you live in and the tire you are using. A general rule of thumb is to refresh sealant when it no longer provides sealing capability, often between 3 to 6 months, or when a significant loss of sealant happens such as when the sealant flows out before fully sealing a puncture or after a burp in the tire.