Clue creates estimates and predictions by continuously analyzing the data you enter.
At the beginning of each cycle, Clue forecasts your date of ovulation as 13 days before the end of your average cycle length. Clue also forecasts your fertile window around its estimate for your date of ovulation.
At the actual end of a cycle (when you have indicated that a new period has started), Clue will retroactively recalculate your date of ovulation to 13 days before the end of this past cycle and adjust your fertile window accordingly.
Your predicted period and fertile window are represented by circles in your calendar. After the recalculation, the circles will be replaced by solid rectangles.
Most of Clue's predictions are based on a limited set of your past data that is determined as most relevant for predictions. This method ensures that Clue adapts to short term environmental factors, as well as longer term changes, as your body moves through different life stages.
Cycle length - Estimates for your cycle length are calculated from a limited set of past data.
Period length - Estimates for your period length are calculated from a limited set of past data.
PMS length and placement - Estimates for your PMS length and position are calculated from a limited set of past data.
Ovulation - Estimates for your day of ovulation are determined by counting backwards 13 days from your average cycle length. Clue may use a different value, if your BBT data or a "ovulation test pos." tag indicate otherwise. This means Clue's estimate of your actual day of ovulation improves at the end of each cycle.
Clue uses this method of counting backwards because counting forwards from the first day of your period is inaccurate for any person who has a cycle length different from 29 days.
This is crucial to understand for people who use ovulation and fertile window estimates for conception or contraception purposes. Do not use Clue as a contraceptive.
Fertile window - Your fertile window is estimated as being from 4 days prior to ovulation to 1 day past ovulation, including the day of ovulation.
For more information, please see the informational text in the app. You find it by tapping the "i" on the Current Cycle screen while the fertile window is selected.