Terms of Use
Last updated 19 August 2026
1. Using the site
By using Period Calculator you accept these terms. If you do not accept them, do not use the site. It is free, needs no account, and you may stop using it at any time by closing the tab.
2. Not medical advice
The dates, ovulation day, fertile window and cycle-day figures shown are general reference information produced by a calendar calculation. They are not a diagnosis, a prescription, or a substitute for a consultation. If your cycles are painful, absent, unusually heavy, suddenly irregular, or you are trying to conceive or think you may be pregnant, speak to a doctor, midwife, nurse or pharmacist. Never delay seeking medical care because of something this page showed you.
3. Not contraception
Calendar-based fertility estimates are not a reliable way to avoid pregnancy. Ovulation moves between cycles, and sperm can survive for several days, so the real fertile period may fall outside the window drawn here. Do not rely on this tool for contraception. Ask a healthcare professional about methods that suit you.
4. Estimates, not facts
Predictions are only as good as the averages you enter, and real cycles shift with stress, illness, travel, weight change, breastfeeding, perimenopause, hormonal contraception and other factors. Later cycles in the table are less reliable than the next one, which is why irregular mode widens the range as it projects further ahead. Treat every date as an estimate.
5. Your data is yours
Calculations run in your browser and nothing is uploaded, so you are the only holder of what you enter. That also means we cannot recover it for you. If you clear your browser storage, use a different device, or use private browsing, your saved dates and notes are gone. Keep your own record of anything you need to keep. See the privacy policy for exactly what is stored.
6. Availability and changes
The site is provided as is. We may change, move or withdraw it, or change these terms, without notice. We do not promise it will always be reachable or free of errors.
7. No warranty
To the fullest extent permitted by law, Period Calculator is provided without warranties of any kind, express or implied, including fitness for a particular purpose and accuracy of results.
8. Limitation of liability
To the fullest extent permitted by law, we are not liable for any loss or damage arising from your use of, or reliance on, this site or its predictions. This includes unplanned pregnancy, missed appointments, treatment decisions and lost data. Nothing here limits liability that cannot lawfully be limited, and nothing in these terms affects your statutory rights.
9. Acceptable use
Use the site for your own personal reference. Do not attempt to disrupt it, overload it, or present its output as professional medical guidance to other people.
10. Links to other services
The calendar buttons open Google Calendar or Outlook. Those services are run by other companies, under their own terms and privacy policies, and we are not responsible for them.
11. Contact
See the contact page.