Founding batches, November and December 2026: half price on the PCOS Reset Cohort. See the cohort →
Founding batches, November and December 2026: half price on the PCOS Reset Cohort. See the cohort →
Free tool · private
Enter the first day of your last period and your usual cycle length to estimate your due date.
Written by the Femwise editorial team · Updated 7 October 2026 · Our reviewers check the medical facts on this page; they don't review or endorse our products.
Quick answer
A due date is usually estimated by adding 280 days (40 weeks) to the first day of your last period, assuming a 28-day cycle. Because periods can be irregular, especially with PCOS (now called PMOS), a first-trimester ultrasound dates a pregnancy most accurately, and your doctor may change the date after it.
How it's calculated
Due date = first day of your last period + 280 days + (your cycle length − 28 days)
Example: if your last period started on 1 November 2026 and your cycle is 28 days, your estimated due date is 8 August 2027. With a 35-day cycle, it moves to 15 August 2027.
With PCOS, cycles are often long or irregular, so a date-based estimate can be out by a week or more. Tell your doctor about your cycles; an early ultrasound gives a more reliable date.
⚠ When to get help straight away
Go to a hospital, or call 112 or your state's ambulance number (108 or 102 in most states), if you have bleeding from the vagina, severe belly pain, a severe headache with blurred vision, fits, sudden swelling of the face or hands, a fever, fast or difficult breathing, leaking fluid, or, later in pregnancy, your baby moving less than usual.
Questions
How accurate is a due-date calculator?
It gives an estimate. Most babies are born between 37 and 42 weeks, and an early ultrasound dates a pregnancy more accurately than dates alone.
What if I don't remember my last period?
Your doctor can date the pregnancy with an ultrasound.
Can I use it after IVF?
After IVF, the due date is worked out from the embryo transfer date, so ask your fertility clinic for yours.
Is EDD the same as the due date?
Yes. EDD stands for estimated date of delivery.
Sources
· Methods for estimating the due date, ACOG Committee Opinion 700
For general information; it doesn't replace advice from your own doctor. Medical disclaimer
