Calculate Your Pregnancy Due Date.

Your due date is calculated using Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day cycle with ovulation on day 14. Our calculator adjusts for your actual cycle length — if your cycle is 32 days, 4 days are added; if 24 days, 4 days are subtracted.

Naegele's rule is the standard method for estimating due dates: LMP + 7 days − 3 months + 1 year = due date (equivalent to LMP + 280 days). It's a population-level estimate; only about 4–5% of babies arrive on their exact due date. Accuracy improves with early ultrasound confirmation (±3–5 days at 7–13 weeks).

Cycle length shifts ovulation timing, which changes the conception date. The standard 280-day formula assumes ovulation on day 14. For a 32-day cycle (ovulation ~day 18), add 4 days to the due date. For a 24-day cycle (ovulation ~day 10), subtract 4 days. Our calculator automatically applies this adjustment when you enter your average cycle length.

When conception date is known (via ovulation tracking, BBT, or OPKs), the due date is calculated by adding 266 days (38 weeks) from conception. This is more precise than LMP-based dating because it removes the variability of cycle length and ovulation timing. Our conception date method uses this 266-day formula.

IVF due dates are calculated from the embryo transfer date based on embryo age at transfer. For a 5-day blastocyst transfer, add 261 days (37 weeks + 2 days). For a 3-day cleavage-stage transfer, add 263 days (37 weeks + 4 days). These intervals align with ASRM and SART guidelines and account for the embryo's developmental age before transfer.

Gestational age counts from the first day of your LMP (approximately 2 weeks before conception) and is the standard used by healthcare providers. Fetal age (embryonic age) counts from the actual conception date. Our calculator displays gestational age — this is why you may be '4 weeks pregnant' before implantation occurs.

Due date calculators provide estimates based on population averages. Early ultrasound (crown-rump length at 7–13 weeks) is the gold standard with ±3–5 day accuracy. LMP-based calculators can be off by 1–2 weeks, especially with irregular cycles, recent hormonal birth control, or uncertain LMP recall. Always confirm dating with your provider via ultrasound.

Yes. If early ultrasound dating differs from your LMP-based due date by more than 5–7 days (first trimester) or 10–14 days (second trimester), your provider will typically update your due date to match the ultrasound. First-trimester ultrasound is most reliable for dating; later ultrasounds assess growth rather than establish dates.

Trimesters divide the 40-week gestational period: First trimester (weeks 0–13) covers organogenesis; second trimester (weeks 14–27) includes anatomy scan and quickening; third trimester (weeks 28–40) covers lung maturation and weight gain. Full term is 39–40 weeks; early term 37–38 weeks; late term 41 weeks; post-term ≥42 weeks. Our calculator shows your current trimester and progress bar.

Only ~4–5% of babies arrive on their exact due date. Most deliver between 39–41 weeks. If you reach 41 weeks (late term), your provider will discuss monitoring (non-stress tests, biophysical profile) and may recommend induction. At ≥42 weeks (post-term), induction is typically advised due to increased risks. Always follow your provider's guidance for post-dates management.