trackle is reliable from the first cycle onwards, because trackle does not evaluate the cycle based on forecasts, but on the basis of your data,meaning your core body temperature and your entries on the cervical mucus. trackle evaluates your cycle using the symptothermal method. Here you can find out more about how trackle evaluates.
In addition to the evaluation, trackle also shows you prognoses (starting in the 2nd trackle cycle): The prognoses will become more precise the longer you use trackle and will help you to know beforehand when you are likely to be fertile and when not.
BUT: prognoses are not 100% certain predictions of your cycle, they are just predictions. On this page you can find out more about the forecasts and your first trackle cycle.