If you wish to change the cycle length you entered at startup, you can do so by inputting your past period into the calendar tab. Select Calendar, then Edit Period. Select the first day of your last period in the calendar.  This will automatically update the cycle length you entered at startup, and as a result, you may see your fertile window prediction move based on this new information.  You can enter up to 90 days of past period information which will be factored into the fertile window prediction for your first cycle. Alternatively, if you selected that you were not sure what your cycle length was during the account creation process but want to go back and add previous period data, this will also override the “not sure” selection and update your period lengths according to the information you enter in the calendar.  The kegg app will learn your estimated cycle length over time and adjust as needed.