We know that everyone's cycle is different, that's why we offer changes up to 50 days!
To change your cycle length, go to Settings > Averages > Cycle Length (you may have to temporarily switch to Manual tracking to do this).
From here you can adjust the length of your cycle based on what's right for you. You can also change your averages for period length, ovulation and PMS length. Cycles will update your current cycle and future forecasts as soon as you press Done.