Enter the first day of your last period, the date of conception or your IVF transfer date to see your estimated due date, how many weeks pregnant you are today, and the dates each trimester starts.
This is an estimate for general information. It is not medical advice. Only your doctor, midwife or maternity unit can confirm your due date, usually with a dating scan. Terms of use.
How the due date is worked out
From your last period, we add 280 days (40 weeks) to the first day of the period, then add or take away the difference between your cycle length and 28 days. From a conception date we add 266 days (38 weeks). From an IVF transfer we add 261 days for a day 5 embryo or 263 days for a day 3 embryo. Weeks of pregnancy are then counted from the matching first day of the last period, the way maternity services count them.
Example. The first day of your last period was 1 January 2026 and your cycle is 28 days. Adding 280 days gives a due date of 8 October 2026. On 1 March 2026 you would be 8 weeks and 3 days pregnant, in the first trimester. The second trimester starts on 2 April 2026 and the third on 16 July 2026.
Longer cycle. With a 32-day cycle, ovulation is likely about 4 days later, so the due date moves to 12 October 2026.
IVF. A day 5 embryo transferred on 20 January 2026 gives a due date of 8 October 2026.
Sources
Rules checked against the sources below. Every figure is listed on rates and sources.
The usual method, Naegele's rule, adds 280 days (40 weeks) to the first day of your last period. That assumes a 28-day cycle with ovulation around day 14. If your cycle is longer or shorter, the date moves by the difference. If you know the date of conception, add 266 days (38 weeks).
How accurate is a due date?
It is an estimate. Only a small share of babies arrive on the due date itself. A pregnancy counts as full term from 37 weeks, and most babies are born between 37 and 42 weeks. Your dating scan, usually in the first trimester, gives a more reliable date than your last period.
Why is pregnancy counted from my last period?
Because the first day of a period is a date most people know, while the date of conception usually is not. So at conception you are already counted as about 2 weeks pregnant, and a pregnancy is 40 weeks from the last period but about 38 weeks from conception.
How is the due date worked out after IVF?
From the embryo transfer date. For a day 5 embryo (blastocyst), the due date is 261 days after the transfer. For a day 3 embryo, it is 263 days. Your fertility clinic will give you the date it uses.
When does each trimester start?
We use: first trimester up to the end of week 12 (12 weeks and 6 days), second trimester from 13 weeks to the end of week 27, and third trimester from 28 weeks to the birth. Some sources split the weeks slightly differently.
When does maternity leave start?
Maternity leave starts between 2 and 16 weeks before the end of the week your baby is due, and Maternity Benefit is paid for 26 weeks. Use the button under the results to see your leave dates and payments with this due date.
