Menstrual Cycle Length & Ovulation

Hi everyone! I just wanted to get some insight and feedback from others about menstrual cycle lengths and ovulation. I use this app consistently when logging my periods and I want to make sure my period lengths are regular. My period lengths seem to vary; some from 21 days and others to 27. Is this normal? Eventually, I would love to conceive and I just want to make sure that this wasn’t something that could effect my chances of pregnancy as the length of my cycles shift from time to time. Thanks so much!