Pregnancy Due Date Calculator
Estimate due date, gestational age, trimester, conception window, IVF transfer dating, ultrasound-based dating, and pregnancy milestone dates.
Last Updated: June 24, 2026
Estimated Due Date Only
Use this for planning conversations. Your OB/GYN or midwife may revise dating based on ultrasound, cycle history, IVF records, or clinical context.
Dating Inputs
Calendar estimateUsually today's date.
Use 28 if cycles are regular and typical.
Pregnancy Dating Disclaimer
This calculator provides educational estimates only and is not medical advice. Use the estimated due date assigned by your OB/GYN, midwife, fertility clinic, or qualified healthcare professional for prenatal care, testing windows, and delivery planning.
Professional Review Status
This YMYL page has internal methodology review, but no external credentialed professional review is recorded yet.
- Reliance status
- Credentialed health review required before medical reliance
- Required credentials
- licensed physician, registered dietitian, qualified clinician
- Review scope
- screening limitations, nutrition or body-composition assumptions, safety warnings, contraindication language, and medical disclaimer placement
Current reviewer: Iliyas Khan, Internal healthcare operations and claims-context reviewer (HIPAA Compliance Certified).
This page is for general education and planning. It is not medical diagnosis, treatment, nutrition therapy, or a substitute for care from a qualified clinician.
Health credentialed review: professional reliance limit
This page is for general education and planning. It is not medical diagnosis, treatment, nutrition therapy, or a substitute for care from a qualified clinician. Results should be treated as a preliminary estimate, not a filing instruction, diagnosis, product recommendation, eligibility decision, or compliance sign-off. Required professional review: licensed physician, registered dietitian, qualified clinician. Source expectation: Review should cite public-health, academic, medical, or recognized clinical sources for formulas and safety thresholds.
Checked by Iliyas Khan
Pregnancy Due Date Calculator is checked for formula labels, source links, and result limits.
Iliyas Khan, Chief Operating Officer. Updated June 24, 2026. Scope: health calculators.
Health credentialed review: Named internal reviewer: Iliyas Khan, Chief Operating Officer. External credentialed professional review is still required before this page is treated as professional advice.
Internal healthcare operations and claims-context reviewer. Review scope: non-clinical healthcare operations context, insurance/claims language, calculator limitations, and escalation warnings.
Credentials on file: HIPAA Compliance Certified.
Relevant review context: Medical Billing Subject Matter Expert with 5+ years of hands-on RCM experience; Medical billing and coding experience: CPT, ICD-10, and HCPCS; Healthcare revenue cycle management, claims, denial management, and compliance workflow experience.
Required professional credentials: licensed physician, registered dietitian, qualified clinician. Scope: screening limitations, nutrition or body-composition assumptions, safety warnings, contraindication language, and medical disclaimer placement.
This page is for general education and planning. It is not medical diagnosis, treatment, nutrition therapy, or a substitute for care from a qualified clinician.
How to Use This Calculator
Step 1: Choose a dating method
Select last period, conception date, IVF transfer, ultrasound, or known due date.
Step 2: Enter the date details
Provide the method-specific date and cycle length, embryo age, or ultrasound gestational age when needed.
Step 3: Set the as-of date
Use today or another date to calculate gestational age and days until due date.
Step 4: Review the result
Check estimated due date, pregnancy week, trimester, conception window, and milestone table.
How This Calculator Works
The calculator normalizes each dating method into an estimated gestational start date and a 40w0d estimated due date. For last menstrual period dating, it uses 280 days from LMP and adjusts for cycle lengths above or below 28 days. For conception dating, it adds 266 days to the conception date.
IVF mode uses the embryo transfer date and embryo age. Ultrasound mode uses the scan date and measured gestational age to estimate the remaining days to 40w0d. Reverse mode starts from a known due date and works backward to estimate LMP and conception timing.
All date math uses calendar-day calculations. The output should be treated as a planning estimate until confirmed by a qualified prenatal care team.
Core formulas: LMP dating adds 280 days to the first day of the last menstrual period, conception dating adds 266 days to estimated ovulation/conception, and ultrasound mode adds the remaining days from measured gestational age to 40w0d.
What You Need to Know
1) Which Dating Method Should You Use?
The best input depends on what information is reliable. If the first day of the last menstrual period is known and cycles are regular, LMP dating is a common starting point. If ovulation was tracked, conception dating may be more specific. For IVF pregnancies, embryo transfer records are usually the most relevant starting point.
Ultrasound can confirm or revise dating, especially early in pregnancy. ACOG notes that first-trimester ultrasound is the most accurate method to establish or confirm gestational age. Later scans can still help, but they have wider dating uncertainty.
| Method | Formula basis | Best use |
|---|---|---|
| Last menstrual period | Adds 280 days to LMP, with optional cycle-length adjustment. | Best when cycles are regular and the LMP date is reliable. |
| Conception / ovulation | Adds 266 days to estimated conception date. | Useful when ovulation was tracked, but still approximate. |
| IVF transfer | Uses embryo age and transfer date. | Useful for ART pregnancies where transfer records are known. |
| Ultrasound dating | Uses scan date plus remaining days to 40w0d. | Early ultrasound is usually the most accurate dating input. |
| Known due date | Works backward to estimate LMP and conception window. | Useful when a clinician has already assigned an EDD. |
2) Worked Dating Examples
Due-date math is calendar-based, but the best input depends on the reliability of the record. These examples show how the calculator handles common user situations.
| Scenario | Input example | Interpretation |
|---|---|---|
| LMP estimate | First day of last period: Jan. 1, 2026; 28-day cycle | EDD is Oct. 8, 2026 because standard LMP dating adds 280 days. |
| Longer cycle adjustment | First day of last period: Jan. 1, 2026; 32-day cycle | EDD shifts about 4 days later because ovulation is estimated later than in a 28-day cycle. |
| Conception estimate | Estimated conception or ovulation: Jan. 15, 2026 | EDD is about 266 days later; use this only when ovulation timing is reasonably known. |
| Known clinical EDD | Clinician-assigned EDD entered directly | The calculator works backward for week and milestone planning, but the clinical EDD remains the controlling date. |
3) Understanding Gestational Age
Gestational age counts from the estimated first day of the last menstrual period, not from conception. This is why conception usually occurs at about 2w0d gestational age in a typical 28-day cycle. The calculator reports both estimated conception date and gestational age so the two timelines are not confused.
A due date is an estimated date of delivery. Many pregnancies deliver before or after the exact date. Prenatal care teams use the assigned EDD to schedule screening windows, interpret fetal growth, and plan follow-up.
| Milestone | Timing | Meaning |
|---|---|---|
| Estimated conception | About 2w0d gestational age | Approximate timing, not proof of exact conception. |
| First trimester ends | 13w6d | Second trimester starts at 14w0d. |
| Third trimester starts | 28w0d | Late pregnancy stage begins. |
| Full-term window starts | 39w0d | Common clinical language for full term starts here. |
| Estimated due date | 40w0d | Planning date, not a guaranteed delivery date. |
4) When to Trust Clinical Dating Over a Calculator
Use clinician dating when it differs from a simple calendar estimate. Your care team may have access to ultrasound measurements, IVF documentation, cycle history, exam findings, or prior records that make the official EDD more reliable than a standalone calculator.
Contact your healthcare professional promptly for bleeding, severe pain, decreased fetal movement later in pregnancy, persistent vomiting, high blood pressure symptoms, or any urgent concern. This page is a planning tool, not a triage tool.
| Question | Practical answer |
|---|---|
| Most practical starting point | Use the method with the most reliable record: clinic-assigned EDD, IVF records, early ultrasound, reliable LMP, or tracked ovulation. |
| When dates conflict | Ask the prenatal care team which EDD controls records and testing windows instead of averaging multiple calculator outputs. |
| What not to infer | Do not use conception-window output as proof of exact conception, paternity, viability, or delivery date. |
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Sources & References
- 1.ACOG - Methods for Estimating the Due Date(Accessed June 24, 2026)
- 2.Johns Hopkins Medicine - Calculating a Due Date(Accessed June 24, 2026)
- 3.ACOG - Definition of Term Pregnancy(Accessed June 24, 2026)