Pregnancy Due Date Calculator

About the Pregnancy Due Date Calculator

Estimate when your baby is due and how far along you are. Enter the first day of your last period — or your conception date or IVF transfer date — to see the estimated due date, your current week and trimester, and key dates along the way.

If your cycles are longer or shorter than 28 days, enter your usual cycle length for a more accurate estimate.

How does the Pregnancy Due Date Calculator work?

Pregnancy is counted from the first day of the last period, about two weeks before conception. A pregnancy lasts on average 280 days (40 weeks) from that day — the rule doctors call Naegele’s rule.

For a cycle longer or shorter than 28 days, the date is moved by the difference. From a known conception date the due date is 266 days later; after an IVF transfer it is 263 days after a day-3 embryo transfer and 261 days after a day-5 transfer.

Pregnancy Due Date Calculator formula

due date = first day of last period + 280 days + (cycle length − 28)
due date = conception date + 266 days

Example

A last period starting on 1 March with a 28-day cycle gives a due date of 6 December. With a 32-day cycle it moves 4 days later, to 10 December.

Tips

• Your first ultrasound scan gives the most reliable dating — use the date your midwife or doctor confirms.
• Plan for any time from 37 to 42 weeks: only a small share of babies arrive on the due date itself.