Your fertile window prediction could be very close to your period dates for several reasons. This can happen if you have short cycles, highly variable cycles, or atypical cycles in your tracking history that are affecting predictions. It can also occur if you have relatively long periods.
Information for short cycles:
If your cycles are around 24 days, there may be only a few days—or no days—between the last day of your period and the start of your predicted fertile window. In very short cycles, there may even be an overlap.
The fertile window shown in the Clue app is always 7 days, regardless of cycle length. This is because of how long sperm can survive in the female reproductive tract, and that the egg can survive approximately 1 day after ovulation. With the fertile window always being 7 days, the chances of your period and fertile window overlapping are higher if you have fewer days in your cycle.
No matter how short or long your cycle is, the Clue algorithm performs in the same way. It estimates your fertile window by calculating the days within your cycle when pregnancy is most likely to occur.
Information for atypical cycles:
If you don’t have short cycles, it could be that previous cycles are affecting Clue’s calculations. This can happen when an atypically short or long cycle is tracked in your last 12 cycles. Experiences like pregnancy, miscarriage, forgetting to track a period, use of emergency contraception, abortion, or using hormonal birth control to skip a period can lead to this.
When these experiences occur, we recommend hiding the corresponding cycle from your Clue calculations to improve your averages and predictions. If you generally experience highly variable cycles though, we recommend keeping these cycles visible in your tracking history for your health records.
Here’s how you can check for atypical cycle lengths:
- Open your Analysis Tab (bottom navigation menu, second icon from the right).
- Scroll down to your ‘Cycle history’.
- Look for a cycle that was much shorter or longer than usual in your last 12 cycles.
- If you find an atypical cycle, tap on the three dots to the right of the cycle dates.
- Toggle on “Hide this cycle” at the bottom of the screen.
Once hidden, this cycle will appear grayed out in your analysis overview, and your fertile window predictions should update accordingly.
It’s important to remember that the fertile window is an estimation only and should not be used to prevent pregnancy. Your body is not a clock, and you may ovulate on different days each cycle, which the Clue algorithm cannot always account for. You can read more about it here.