Looking for a reliable Pregnancy Due Date Calculator? Use our ACOG-based calculator above to estimate your baby’s due date from LMP, Ultrasound, Conception/IUI, or IVF transfer in seconds. It’s private (runs in your browser), ultra-fast, and designed for global users. Below, you’ll find everything you need to understand how due dates work, how accuracy varies, and how to read your results—so you can plan with confidence.

Quick answer: Most people start with LMP (last menstrual period) and add 280 days (40 weeks). If you have an early ultrasound, that’s often the most precise basis. For IVF, due dates depend on embryo age at transfer (commonly Day-5 + 261 days). Always confirm with your clinician.

Pregnancy Due Date Calculator

Q: Can I trust an online Pregnancy Due Date Calculator?

Yes—as an estimate . Our calculator uses widely accepted medical conventions for LMP, ultrasound, conception/IUI, and IVF. Accuracy depends on your input and timing; early ultrasound is typically the most precise. Always confirm with your clinician.

Q: My cycles aren’t 28 days. How does the calculator adjust?

If you choose LMP , you can set your cycle length . We shift the due date by (cycle length − 28) days to better reflect your likely ovulation timing.

Q: Ultrasound vs. LMP: which should I rely on?

If there’s a significant difference—especially with an early scan—clinicians often adopt the ultrasound date. Bring both to your appointment and ask which basis your provider prefers.

Q: I did IVF. Which option should I choose?

Choose IVF and select the correct embryo day: Day-5 (most common) adds 261 days , Day-3 adds 263 , and Day-6 adds 260 from transfer.

Q: Will you store my dates or personal details?

No. The calculator runs entirely in your browser . We don’t transmit or store your inputs.

Clinically standard formulas (ACOG) for LMP, Ultrasound, Conception/IUI, and IVF (Day-3/5/6). No data stored.

Method Pick the method you know best; ultrasound/IVF are typically most precise early.

First day of LMP

Cycle length (days)

We don’t send or store inputs. Everything runs locally in your browser.

Estimated Due Date

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Due-week window appears after calculation.

How far along

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Trimester: —

Key Milestones

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Method

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About these calculations ACOG-based

• LMP +280d (adjust for cycle length). • Ultrasound: EDD = scan date + (280 − GA at scan). Accuracy best in 1st trimester (±5–7d). • Conception/IUI +266d. • IVF: Day-3 +263d, Day-5 +261d, Day-6 +260d.

These are estimates; most babies don’t arrive exactly on the EDD. Always confirm with a clinician.

Educational only. Not a diagnostic device. For medical decisions, consult your OB/GYN or midwife.

Why our Pregnancy Due Date Calculator stands out

Clinically standard rules: Built around widely used obstetric conventions for LMP, ultrasound “redating,” conception/IUI, and IVF (Day-3/5/6).
Multiple methods: Many calculators support only LMP; we support four clinically relevant pathways so more users get an accurate estimate.
No data collection: Everything calculates locally in your browser—fast, private, and globally accessible on any device.
Clear expectations: We show a due-week window and trimester context, because only a minority deliver exactly on their EDD.
Global, lightweight UX: Zero external libraries for speed, accessibility-minded markup, and mobile-first design to protect Core Web Vitals.

Planning the rest of your pregnancy? Try our other tools too:
• AI Prescription Checker — understand prescriptions in plain language
• Symptom Checker — explore possible causes for common symptoms
• Pill Identifier — identify pills by imprint, color, and shape

How the calculator works (plain-English guide)

1) By LMP (most common):
Enter the first day of your last menstrual period. Standard dating adds 280 days (40 weeks). If your cycle isn’t 28 days, the calculator adjusts by the difference (e.g., 32-day cycles shift +4 days; 24-day cycles shift −4). This matches how many clinicians account for ovulation timing relative to cycle length.

2) By Ultrasound (often most precise early):
If you have an early ultrasound, our Pregnancy Due Date Calculator uses your scan date plus the gestational age (weeks + days) measured on that scan to compute your EDD. Early ultrasounds (especially in the first trimester) tend to be accurate within about a few days, and they are commonly used to “redate” the pregnancy if LMP and ultrasound disagree beyond specific thresholds.

3) By Conception/IUI date (known ovulation):
If you know the exact conception or IUI date, the due date is calculated as +266 days (38 weeks) from that date. This approach assumes you’re certain of ovulation/insemination timing.

4) By IVF/ART transfer:
For IVF, your EDD depends on embryo age at transfer. A common scenario is Day-5 embryo + 261 days; Day-3 embryos use +263 days; Day-6 transfers use +260 days. We include these options so IVF families can date consistently with clinical norms.

Tip: If you have both LMP and a first-trimester ultrasound, use the ultrasound method in the calculator and discuss any differences with your healthcare provider. Early scans are typically the most reliable for dating.

How accurate is a Pregnancy Due Date Calculator?

A due date is a best estimate, not a guarantee. Most babies don’t arrive exactly on EDD. That’s why our calculator also surfaces a window around your EDD to set better expectations. Several factors influence accuracy:

Method used: Early ultrasound is generally the most accurate single input for dating.
Cycle variability: Using LMP assumes a regular 28-day cycle, which isn’t true for everyone; our cycle-length adjustment helps.
Timing of scan: Ultrasound dating is most precise in the first trimester; later scans have wider margins of error.
Embryo age (IVF): Using the correct embryo day (3, 5, or 6) ensures your IVF due date aligns with clinical practice.

For educational background or to read general guidance, you can consult reputable health organizations such as the American College of Obstetricians and Gynecologists (ACOG) and the World Health Organization (WHO). Use our results as an informed starting point, then confirm with your clinician.

Understanding your results: weeks, trimesters, and milestones

Your results panel shows:

Estimated Due Date (EDD): The specific calendar date.
How far along you are today: Weeks + days (e.g., 12w4d).
Trimester: First (0–13w6d), Second (14–27w6d), or Third (28w+).
Key milestones: Helpful time points like ~12 weeks, the anatomy scan window (~18–22 weeks), entry into the third trimester (~28 weeks), and the “full-term” window (~39–40w+6d).

These cues help you plan appointments, travel, and work commitments with a realistic view of what’s ahead.

When to use each method

Use LMP if your cycles are regular and you know your dates.
Prefer ultrasound if you have an early scan; it may replace LMP dating when the difference exceeds typical thresholds.
Use conception/IUI if ovulation was precisely timed.
Use IVF with the correct embryo day (3, 5, or 6) for the most consistent result.

If your LMP-based EDD and ultrasound-based EDD don’t match, your healthcare provider may choose the ultrasound date, especially when the discrepancy crosses standardized limits early in pregnancy.

Related tools

Internal resources:
• AI Prescription Checker
• Symptom Checker
• Pill Identifier
Authority resources:
• ACOG — practice guidelines and patient education
• WHO — global maternal health information

FAQs: Pregnancy Due Date Calculator

Can I trust an online Pregnancy Due Date Calculator?

Yes—as an estimate. Our calculator uses widely accepted medical conventions for LMP, ultrasound, conception/IUI, and IVF. Accuracy depends on your input and timing; early ultrasound is typically the most precise. Always confirm with your clinician.

My cycles aren’t 28 days. How does the calculator adjust?

If you choose LMP, you can set your cycle length. We shift the due date by (cycle length − 28) days to better reflect your likely ovulation timing.

Ultrasound vs. LMP: which should I rely on?

If there’s a significant difference—especially with an early scan—clinicians often adopt the ultrasound date. Bring both to your appointment and ask which basis your provider prefers.

I did IVF. Which option should I choose?

Choose IVF and select the correct embryo day: Day-5 (most common) adds 261 days, Day-3 adds 263, and Day-6 adds 260 from transfer.

Will you store my dates or personal details?

No. The calculator runs entirely in your browser. We don’t transmit or store your inputs.

How to get the most from this page (pro tips)

Bookmark this page and re-check milestones each month.
Share your results (copy/print buttons) with your partner or birth team.
If you get a new ultrasound, re-run the calculator using the scan method to compare dates.
Explore our related tools to prepare for medications, symptoms, or pill identification as pregnancy progresses.

Our Pregnancy Due Date Calculator combines clinical realism with a clean, fast, mobile-first experience. Use it as a trusted starting point, then discuss your personalized timeline with your healthcare provider. Whether you’re dating by LMP, ultrasound, conception, or IVF, you’ll get a transparent estimate, trimester context, and milestone guidance—without sacrificing privacy or performance.