Pregnancy Due Date Calculator
Choose LMP, a known conception date, or an IVF embryo transfer date. The calculator shows your estimated due date, current gestational age, trimester, time remaining, and ACOG term category in one place.
Dating method and date
Choose the first day of your last period to see the result instantly.
Result
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- Gestational age
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- Trimester
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- ACOG term category
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- Dating method
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- Time to due date
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- Conception date
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This result applies ACOG pregnancy-dating guidance as a reference estimate. It is not a diagnosis or personalized medical advice. Confirm your official due date, prenatal schedule, and delivery plan with your obstetric care team.
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How to estimate a due date and gestational age from three known dates
This Pregnancy Due Date Calculator starts with the record you actually have: the first day of your last menstrual period (LMP), a known conception date, or an IVF embryo transfer date. It then places the estimated due date, current gestational age, trimester, time remaining, conception date, and ACOG term category on the same result panel.
Each method uses a distinct formula. LMP adds 280 days and adjusts for the difference from a 28-day cycle; known conception adds 266 days. IVF accounts for development before transfer, adding 261 days after a day-5 transfer or 263 days after a day-3 transfer. Current gestational age runs from the start established by the selected method to today.
A calculator cannot replace an established clinical due date. ACOG identifies ultrasound through 13 6/7 weeks as the most accurate way to establish or confirm gestational age. If your date is uncertain or differs from the date assigned by your care team, use the clinician-established date.
Choose the dating method first
Use the most specific record available for the pregnancy.
- LMP: use when the first day of the last period and average cycle are known.
- Conception: use when fertilization date is specifically known.
- IVF transfer: use the transfer date together with day-3 or day-5 embryo age.
Three formulas, one worked example
Different records for the same pregnancy converge on the same date.
- LMP January 1, 2026, 28-day cycle: due October 8, 2026.
- Conception January 15, 2026: due October 8, 2026.
- Day-5 transfer January 20, 2026: due October 8, 2026.
- Day-3 transfer January 18, 2026: due October 8, 2026.
LMP and cycle adjustment
The 280-day rule assumes a 28-day cycle and ovulation on day 14.
- EDD = LMP + 280 days + (cycle − 28 days).
- A 35-day cycle moves the date seven days later.
- A 21-day cycle moves it seven days earlier.
- An irregular cycle cannot be made exact with this adjustment alone.
IVF day-3 and day-5 dating
ART dating uses the known transfer date and embryo age.
- Day 5: EDD = transfer date + 261 days.
- Day 3: EDD = transfer date + 263 days.
- Gestational start is transfer date minus 14 days and embryo age.
- Conception is displayed as transfer date minus embryo age.
Gestational age and trimester
Gestational age runs from the dating start to today, not backward from the due date.
- Read it as completed weeks plus days, such as 12 weeks 3 days.
- The first trimester runs through 13 6/7 weeks.
- The second spans 14 0/7–27 6/7; the third begins at 28 0/7.
- A cycle-adjusted due date passing early does not force the age to “40+ weeks.”
ACOG term categories
Weeks after 37 are not one undivided full-term range.
- Before 37 0/7: preterm range.
- Early term: 37 0/7–38 6/7.
- Full term: 39 0/7–40 6/7.
- Late term: 41 0/7–41 6/7; postterm begins at 42 0/7.
Why early ultrasound matters
Calendar dating and ultrasound do not use the same evidence.
- First-trimester ultrasound uses crown-rump length (CRL).
- ACOG calls ultrasound through 13 6/7 weeks the most accurate dating method.
- CRL gestational-age accuracy is usually ±5–7 days.
- Uncertain LMP or irregular cycles can widen the calendar difference.
Which date should take priority
The reliability of the source record matters.
- For ART pregnancies, use dating derived from embryo age and transfer date.
- Keep a due date established by early ultrasound and your clinician.
- Distinguish a known conception date from an estimated ovulation date.
- Do not revise an established due date solely because a calculator differs.
Read the result in order
Start with the basis before interpreting the numbers.
- Check that LMP, conception, or IVF and embryo age are correct.
- Read the estimated due date separately from today’s actual gestational age.
- Trimester and term category follow elapsed gestational age.
- The copied result includes the dating method used.
Input checks and limits
A quick review prevents common date errors.
- For LMP, enter the first day bleeding began, not the last day.
- For IVF, enter embryo transfer date, not egg retrieval date.
- The tool does not assess fetal health, symptoms, labor, or test results.
- Use your care team for prenatal timing and individualized decisions.
Frequently asked questions
Which date can I use to estimate my due date?
Use the first day of your last menstrual period, a known conception date, or an IVF embryo transfer date. LMP includes a cycle-length adjustment; IVF also uses whether the embryo was day 3 or day 5 at transfer.
How do the three due date formulas differ?
LMP adds 280 days plus cycle length minus 28 days. Known conception adds 266 days. IVF adds 266 days to the transfer date and subtracts embryo age, which is transfer+261 days for day 5 and transfer+263 days for day 3.
What changes if my cycle is not 28 days?
Only the LMP method shifts the due date by the cycle difference. For example, LMP on January 1, 2026 gives October 8 with a 28-day cycle and October 15 with a 35-day cycle.
Why are day-3 and day-5 IVF formulas different?
The embryo has already developed for a different number of days before transfer. Under ACOG ART dating, a day-3 transfer adds 263 days and a day-5 transfer adds 261 days to reach the estimated due date.
How should I read gestational age and the ACOG term category?
Gestational age is completed weeks and extra days from the calculated gestational start. ACOG defines early term as 37 0/7–38 6/7, full term as 39 0/7–40 6/7, late term as 41 0/7–41 6/7, and postterm from 42 0/7.
My ultrasound due date is different. Which one takes priority?
ACOG describes first-trimester ultrasound through 13 6/7 weeks as the most accurate way to establish or confirm gestational age; CRL dating is usually accurate within ±5–7 days. Follow the date your clinician establishes from ultrasound and clinical information.
Do I also need LMP if I know the conception date?
No. Choose the conception tab and enter that date to add 266 days. If you only estimated ovulation rather than knowing fertilization, treat the result as a broader estimate.
Can this result set my prenatal or delivery plan?
No. This tool applies published date formulas for reference. Confirm gestational dating, test timing, symptoms, risk factors, and delivery planning with an obstetric clinician.
Official sources
Evidence scope: ACOG Committee Opinions No. 700 and No. 579 (reaffirmed 2025) and the NHS public explanation. Date calculation for reference as of August 20, 2026; not a medical diagnosis.