28 is typical. Longer cycles push the due date later.
Key dates
Week-by-week timeline (40 weeks)
| Week | Starts | Stage |
|---|
Estimates only. Only about 1 in 20 babies arrive on the due date; most come within two weeks either side. Your first ultrasound (usually 8–14 weeks) gives the most accurate dating — if it differs, use the scan date with the "I know my due date" option.
About Pregnancy Due Date Calculator
This due date calculator works the way your doctor does. From the first day of your last period it uses Naegele's rule (280 days, adjusted if your cycle is not 28 days); from a conception or ovulation date it adds 266 days; and for IVF it counts from the embryo transfer date and the embryo's age on that day, which is the most precise method of all. You get your estimated due date, how many weeks and days pregnant you are today, your trimester, a progress bar, the key appointment windows (12-week scan, anatomy scan, glucose screening, Tdap, group B strep) with their dates, and a full 40-week timeline. Enter a due date from your scan instead and everything recalculates from it. Every result has a shareable link, and nothing you enter is stored or sent anywhere.
How to use it
- Choose how you want to calculate: last period, conception date, IVF transfer, or a due date you already know.
- Enter the date (and your cycle length if it is not 28 days, or the embryo age for IVF).
- Read your due date, current week, trimester and the dated milestones; open the timeline for every week, and copy the link to save or share it.
Frequently asked questions
How accurate is a due date calculator?
The date is an estimate. Only about 4–5% of babies are born on their due date, and most arrive within a two-week window either side. A first-trimester ultrasound (usually between 8 and 14 weeks) dates a pregnancy more accurately than any calculator, so if your scan gives a different date, use that one.
Why does cycle length change the due date?
The 280-day rule assumes ovulation on day 14 of a 28-day cycle. If your cycles are 32 days, you likely ovulated about four days later, so the due date moves four days later too. The calculator shifts the date by the difference between your cycle and 28 days.
How does the IVF option work?
With IVF the fertilisation date is known. The calculator subtracts the embryo's age at transfer (3, 5 or 6 days) to get the conception date, then adds 266 days. This is why IVF due dates are usually more precise than dates from a last period.
What week does each trimester start?
The first trimester runs to the end of week 12, the second from week 13 to 26, and the third from week 27 until birth. Full term is 39 to 40 weeks; 37–38 weeks is called early term.
Is my information stored?
No. The calculation happens in your browser and nothing is sent to a server. The shareable link simply carries the date you entered.
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