Free tool
Pregnancy week calculator
Estimate your due date and current gestational week. Choose the dating method that matches what your clinician used, including IVF transfer and ultrasound. All figures are informational and not a substitute for medical advice.
Estimated due date
Thursday, June 10, 2027
Current
8w 4d
Trimester
1
Days to go
220
Conception
Sep 17, 2026
Week-by-week milestone reference
Factual reference points clinicians commonly track. Individual care plans vary.
Week 4
Missed period. Home pregnancy tests typically turn positive.
Week 8
First prenatal visit common. Embryo measures ~16mm.
Week 12
End of first trimester. Combined screening window (NT scan, 11-14w).
Week 16
Quad screen window opens. Some parents feel quickening.
Week 20
Anatomy scan typical. Anatomical survey checks fetal structures.
Week 24
Viability threshold per most NICUs. Glucose tolerance test soon after.
Week 28
Third trimester begins. Rh immunoglobulin given to Rh-negative parents.
Week 32
Growth scan if indicated. Fetal movement counts often started.
Week 36
Group B strep swab typical. Full-term window begins at 37w.
Week 40
Estimated due date. Only ~5% of births land exactly here.
How pregnancy weeks are counted (it starts before conception)
Clinical pregnancy weeks count from the first day of the last menstrual period (LMP), not from conception. That means by the time a missed period prompts a test, the pregnancy is already dated around week 4. Ovulation and fertilisation happen near the end of week 2 in a typical 28-day cycle, so the gestational-age clock is always about two weeks ahead of the actual embryo's age.
The American College of Obstetricians and Gynecologists (ACOG) recommends estimating the due date as LMP plus 280 days. See the ACOG Committee Opinion on estimating the due date for the full clinical framing.
When to use each dating method
LMP works when periods are regular and the date is known. For cycles that run longer or shorter than 28 days, adjusting the cycle length shifts the implied ovulation date and the due date along with it. Conception-based dating is useful when ovulation was tracked directly. IVF dating is the most precise of all because the embryo's age is known to the day: a day-3 transfer adds 263 days, a day-5 blastocyst transfer adds 261. Ultrasound dating uses the gestational age the sonographer measured (typically from crown-rump length in the first trimester) and is the preferred method when LMP is uncertain or differs from the scan by more than 5-7 days.
The 280-day rule and why it's only an estimate
Only about 5% of births occur exactly on the estimated due date. A term pregnancy is anything from 37 weeks 0 days through 41 weeks 6 days. The 280-day figure is a convention based on average cycle length and average gestation, and individual variation is wide. Treat the date as a centre point, not a deadline. Anything your care team measures with ultrasound or other clinical tools will be more accurate than a calendar calculator like this one.