When you LO is ready. I try on 2yr 8mths she cannot hold her urine yet. So failed. 3yr 3mths she was all ready.. With a diaper but will control and go toilet and we trail with diaper for a week. The following week we go diaper free!! U will know the best for your LO. Every child is different. We can take online or other as a guide but not compare. 😉