Cycle Tracker On-device
Log period start dates to see the estimated next period, ovulation and fertile window — everything stays on your device.
Your data stays on this device — nothing is uploaded, and there's no account.
Logged period starts
No dates logged yet. Log your most recent period start to see estimates.
Settings
Your data
Estimates only — not a contraceptive method and not medical advice. Consult a clinician for family planning.
Private period and ovulation calendar that runs entirely on your device — log period start dates to see the estimated next period, ovulation and fertile window. Nothing is uploaded and there is no account.
About this tool
What you provide
- Your period start dates, logged one at a time
- An average cycle length between 15 and 60 days, or let it be calculated from your logged dates
What you get
- Estimated date of the next period
- Estimated ovulation date and a six-day fertile window ending on it
- A JSON export of your logged dates and settings
Limits
- Estimates only — not a contraceptive method and not medical advice. Consult a clinician for family planning.
- Ovulation is back-calculated from the predicted next period assuming a 14-day luteal phase, so an irregular cycle makes the estimate less reliable.
- Data is stored on this device only — nothing is uploaded, there is no account, and clearing site data deletes it.
How to use it
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Log a period start
Set the date field, which opens on today, to the day your period started and press Log period start; the date joins the list below, newest first.
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Check the cycle length
Under Settings the average cycle length is calculated from the dates you have logged, and you can type your own value between 15 and 60 days to override it.
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Read the estimates
The estimates panel shows the next period, the ovulation date back-calculated from it, and the six-day fertile window that ends on that date.
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Export or delete
Under Your data, Export data (JSON) saves a copy as a file on your device, and Delete all data asks you to tap again to confirm before wiping everything stored here.
Frequently asked questions
How does the cycle tracker estimate ovulation and my fertile window?
You log your period start dates, and it estimates your next period, ovulation, and fertile window from that history; everything stays on your device.
Is my cycle data uploaded anywhere?
No, all entries stay on your device only and are never uploaded.
Can I use this as a contraceptive method?
No, it's an estimate tool only, not a contraceptive method; consult a clinician for family planning.