Time until pregnancy due date
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Countdown to your estimated due date
Enter your EDD (calculated as 280 days from your last menstrual period, or as adjusted by an early-pregnancy ultrasound) and the timer above counts down the days, hours, and minutes remaining. The EDD is a target — only about 5% of births fall exactly on it, and roughly 80% arrive within ±2 weeks.
How the estimated due date (EDD) is calculated
Pregnancy is dated from the first day of the last menstrual period (LMP), not from conception. This convention adds about two weeks to the actual gestational age but is used because the LMP is a reliable date most women can identify, while exact ovulation usually can't be.
The standard formula is Naegele's rule:
EDD = LMP + 7 days − 3 months + 1 year
This is equivalent to LMP + 280 days, assuming a 28-day cycle. Worked example: if your LMP was January 1, 2026, then January 1 + 7 days = January 8; minus 3 months = October 8; plus 1 year = October 8, 2026.
The 280-day figure assumes ovulation on day 14 and conception immediately after. For irregular cycles, longer or shorter than 28 days, an adjustment of ±1 day per day of cycle-length deviation is sometimes applied, but a first-trimester ultrasound is preferred for accuracy.
The three trimesters: what's tracked at each stage
Pregnancy is divided into three trimesters. Each has its own set of routine screening windows and milestones:
| Stage | Weeks | Key milestones & tests |
|---|---|---|
| First trimester | 1–12 | Confirm pregnancy; first prenatal visit (8–10wk); fetal heartbeat detectable on ultrasound from ~6wk; NIPT (cell-free DNA) available from 10wk; combined screening (NT + bloods) at 11–13+6 weeks. Embryonic period ends at 10 weeks; "fetus" from week 11 onward. |
| Second trimester | 13–27 | Anatomy scan at 18–22 weeks (anatomical review; sex identification possible); quickening (feeling movement) typically 16–25 weeks; glucose challenge test for gestational diabetes 24–28 weeks. Viability threshold around 24 weeks. |
| Third trimester | 28–40+ | Anti-D injection at 28–30 weeks if Rh-negative; Tdap vaccine 27–36 weeks; growth scans as indicated; GBS swab at 36–37 weeks; weekly visits from 36 weeks; non-stress tests & biophysical profiles past 40 weeks; induction discussed at 41–42 weeks. |
Timing varies by country and provider; this table reflects mainstream US (ACOG) and UK (NICE/NHS) guidance.
Key facts about due dates & delivery timing
- 40 weeks / 280 days from LMP is the standard EDD; 38 weeks / 266 days from estimated conception.
- ~5% of babies are born on the exact estimated due date.
- ~80% are born within 2 weeks either side of the EDD (38–42 weeks).
- ~10% are preterm (before 37 weeks); ~5–10% post-term (after 42 weeks before induction policies).
- Median pregnancy length for first-time mothers is about 40 weeks + 5 days; for subsequent pregnancies, about 40 weeks + 3 days.
- Twin pregnancies average delivery at 37 weeks; triplets at 32–33 weeks.
Third-trimester preparation timeline
| Weeks remaining | Typical preparation |
|---|---|
| ~12 weeks out (28wk) | Tour birthing facilities; consider birth class; Tdap vaccine window opens. |
| ~8 weeks out (32wk) | Finalize birth plan; install car seat (most hospitals require it); discuss pain-relief options. |
| ~5 weeks out (35wk) | Pack hospital bag; complete GBS swab (35–37wk); arrange childcare/pet care for labor day. |
| ~3 weeks out (37wk) | Baby is now "early term"; weekly OB visits begin; review signs of labor. |
| ~1 week out (39wk) | Membrane sweep may be offered; finalize maternity leave; charge phone & camera. |
| Past EDD (40wk+) | Increased monitoring; induction discussed by 41wk; only 5% of babies arrive exactly on the EDD. |
Limitations of the countdown
- The EDD is an estimate, not a deadline. Only ~5% of babies arrive on that exact date.
- If your EDD was set by LMP and you have an irregular cycle, the true date could be off by a week or more. An early-pregnancy ultrasound usually gives a more accurate revised EDD.
- The countdown doesn't account for medical factors that may bring delivery earlier (preeclampsia, gestational diabetes, IUGR) or later (post-term induction policies).
- This tool is for personal planning — not a substitute for medical advice. Always defer to your provider's dating and care plan.
Sources & references
FAQs
The standard method is Naegele's rule: add 280 days (40 weeks) to the first day of the last menstrual period (LMP), assuming a 28-day cycle. The shorthand is LMP + 7 days − 3 months + 1 year. For conception-based dating, the EDD is roughly 266 days from ovulation. An early-pregnancy (first-trimester) ultrasound is more accurate than LMP dating, especially for irregular cycles, and is the gold standard if there's any discrepancy of more than 5–7 days (per ACOG guidelines).
Only about 5% of babies are born on the exact estimated due date. Roughly 80% are born within ±2 weeks of the EDD — that is, between 38 and 42 weeks. Around 10% are preterm (before 37 weeks) and a further 5–10% are post-term (beyond 42 weeks). First-time pregnancies tend to deliver slightly later on average than subsequent pregnancies.
Key timing windows: the first-trimester combined screening (nuchal translucency + blood test) at 11–13+6 weeks; the anatomy scan at 18–22 weeks; the gestational diabetes glucose challenge at 24–28 weeks; the Group B strep (GBS) swab at 36–37 weeks. Tdap vaccine is recommended at 27–36 weeks. NIPT (cell-free DNA) can be done from 10 weeks onward. Refer to your provider's plan — this is general US/UK timing.
ACOG and the WHO use these definitions: extremely preterm before 28 weeks; very preterm 28–32 weeks; moderate to late preterm 32–37 weeks; early term 37–38+6 weeks; full term 39–40+6 weeks; late term 41–41+6 weeks; post-term 42 weeks and beyond. Induction is typically offered between 41 and 42 weeks if labor hasn't started spontaneously.
First-trimester ultrasound (before 14 weeks) is accurate to within roughly ±5–7 days. Second-trimester ultrasound (14–20 weeks) is accurate to ±10–14 days. Third-trimester ultrasound is the least accurate — ±21–30 days. ACOG recommends that if there's a discrepancy between LMP-based and ultrasound-based dating greater than the precision of the scan, the EDD should be adjusted to the ultrasound date.
Going a few days past your EDD is normal — only 5% of babies arrive on the exact day. Most providers offer membrane sweeps from around 39–40 weeks and discuss induction between 41 and 42 weeks. Beyond 42 weeks, risks (stillbirth, oligohydramnios, large-for-gestational-age complications) climb, and induction is typically recommended. Monitoring (non-stress tests, biophysical profiles) increases past the EDD.