Last updated: 20 July 2026
Seek professional advice
Always consult your midwife, obstetrician, GP or another qualified provider about anything concerning your pregnancy, your fertility or your health. Never disregard professional advice, or delay seeking it, because of something you read here. If you are experiencing a medical emergency, contact your local emergency number or go to the nearest emergency department immediately.
Contact your care provider promptly if you experience any of the following during pregnancy. This list is not exhaustive and is included because these are the situations where waiting is the wrong choice:
- vaginal bleeding or fluid leaking
- severe or persistent abdominal pain
- a noticeable reduction or change in your baby's movements
- severe or sudden headache, visual disturbance, or sudden swelling of the face and hands
- fever, or symptoms of infection
- regular painful contractions before 37 weeks
- anything that simply feels wrong to you, even if it is not on this list
Why these results are estimates
Every tool on this site applies a standard formula to the dates you enter. Formulas describe populations, not individuals, and they rest on assumptions that will not hold for everyone.
| Tool | Key assumption | When it will be less accurate |
|---|---|---|
| Due Date Calculator | 280 days from LMP, adjusted for cycle length | Irregular cycles, uncertain LMP, recent hormonal contraception |
| Ovulation Calculator | Ovulation falls a fixed luteal phase before the next period | Irregular cycles, PCOS, breastfeeding, perimenopause, stress or illness |
| Pregnancy Week Calculator | Gestational age counted from LMP; 40-week term | Dating not yet confirmed by scan; twins or higher multiples |
Two figures are worth keeping in mind whenever you look at a result on this site. Only about 4 to 5 percent of babies are born on their estimated due date. And a first-trimester ultrasound — the most accurate dating method routinely available — still carries a margin of roughly five days. If the best clinical tool available has a five-day margin, a calendar calculation cannot do better.
Ultrasound dating takes precedence
If you have had a dating scan, the due date on your maternity notes is your official date. It is the one your appointments, screening windows and clinical decisions are scheduled against. Where this site's result differs, follow your notes. A difference of a few days is normal and clinically unimportant.
Fertility tools are not contraception
The ovulation calculator is designed to help people trying to conceive. It must not be used as a method of birth control. Calendar-based prediction has a high failure rate because ovulation timing shifts with stress, illness, travel, weight change and countless other factors. Fertility awareness methods used for contraception require formal training, daily observation of multiple physical signs, and far wider safety margins than any calculator provides. For reliable contraception, speak to a healthcare provider.
Not for clinical or professional use
These tools are intended for personal, informational use by members of the public. They are not validated medical devices, have not been through regulatory clearance, and should not be used to make clinical decisions or as part of a professional workflow. Healthcare professionals should rely on validated clinical systems and current professional guidance.
Sources and currency of information
Content is written against publicly available professional guidance, including ACOG Committee Opinion 700 on definitions of term pregnancy, ACOG/AIUM/SMFM guidance on estimating the due date, and published prospective studies of day-specific conception probability. Clinical guidance is revised over time, and recommendations vary between countries and between individual practices. A page may not reflect the most recent revision, and we make no warranty that it does. Where a figure is a population average rather than a fixed rule, we try to say so on the page.
Individual variation
Reference ranges, milestone timings and size comparisons describe what is typical. Healthy pregnancies vary enormously, and falling outside a typical range is very often entirely normal. Only your care provider, with the full picture, can interpret what any measurement means for you. Please do not use this site to reassure yourself out of a concern, or to worry yourself into one.
Limitation of liability
To the fullest extent permitted by law, DueDatez and its operators accept no liability for any loss, injury or damage arising from use of, or reliance on, information or calculator results on this site. Your use of the site is entirely at your own risk. This disclaimer forms part of our terms of use and should be read alongside our privacy policy.
Questions
If you think something on this site is inaccurate or misleading, please tell us through the contact form or at corrections@duedatez.online. Corrections are dealt with ahead of everything else.