Sources we use
Medical statements are based on, in order of preference:
- Clinical guidance from professional and public-health bodies, such as the American College of Obstetricians and Gynecologists (ACOG), the World Health Organization (WHO) and the NHS.
- Peer-reviewed research published in medical journals, described as the findings of that study rather than as a promise about any one pregnancy.
Each source is recorded with its title, publisher, date and link. Every page that makes a medical statement shows a numbered Sources list, and each statement links to its source.
How calculations are checked
The calculators only implement rules that have been checked against the sources. Where a value is derived rather than stated directly — for example, the 266-day interval from an estimated conception date to the due date, which is 280 days minus the 14 days the convention assumes before ovulation — the page says so. Features without a verified rule, such as adjusting a due date for cycle length, are not offered. The date arithmetic is covered by automated tests.
How estimates are worded
- Results are called estimates, never exact or guaranteed dates.
- An estimated conception date is always described as an estimate by convention. The site does not make paternity claims.
- How far along a pregnancy is, is shown in completed weeks and days, for example “12 weeks 3 days”.
- Decisions about clinical dating are left to healthcare professionals.
Medical review
Content on this site has not been reviewed by a named doctor or midwife, and the site does not claim otherwise. That is why every medical statement is tied to a source you can check yourself. See the medical disclaimer.
Updates and corrections
Each page that cites sources shows when they were last checked. If a source is updated or an error is found, the affected page and calculation are corrected. To report a possible error, please use the contact page.
Independence
The site currently shows no advertising and has no sponsors, and its content does not promote any product or service. If advertising is ever added, it will be kept separate from the content and this policy will be updated.