The switch from second-tier to third-tier formula is usually made after the child turns one year old. When switching your baby to formula, it is usually necessary to gradually replace the second stage formula with the third stage formula. You can start by replacing the second formula with the third formula once a day. After two to three days, if the child has no adverse reactions, you can add a third formula until the child is fully transitioned to a third formula. You can also add a small amount of third-rate milk powder to the second-rate milk powder each time you brew it, and then gradually increase the amount of third-rate milk powder and decrease the amount of second-rate milk powder after the child gets used to it, until finally the second-rate milk powder is completely replaced by third-rate. The actual time will depend on the child’s ability to adapt.