How predictions work
We estimate the next period from your usual cycle length. Ovulation is then estimated about 14 days before the next period. The fertile window is the 5 days before ovulation plus ovulation day and the following day.
This is a calendar estimate, not a diagnostic fertility test. Irregular cycles, illness, stress, breastfeeding, and hormonal changes can all reduce prediction accuracy.
Privacy and control
All period starts and symptom logs stay in browser storage unless you choose to export them. You can export JSON or CSV, import JSON on another device, and wipe everything by typing CLEAR.
FAQ
How is the next period predicted?
The tracker estimates the next period from your logged or entered cycle length, then counts forward from the last period start date.
How is ovulation predicted?
This tracker assumes ovulation happens about 14 days before the next period, which is a common calendar estimate but not a guarantee.
Can I use this to avoid pregnancy?
No. Calendar-based prediction is not a reliable contraceptive method.
Does my data leave the browser?
No. The tracker stores data in local browser storage and exports only when you choose to download it.
What if my cycles are irregular?
Irregular cycles make date prediction less reliable. If variation is frequent or large, discuss it with a clinician.
Can I move my data to another device?
Yes. You can export JSON from the tool and import it into another browser.