Pregnancy & Baby

Due Date
Calculator

Calculate your baby's due date using 4 methods — LMP, conception date, IVF transfer, or ultrasound weeks. Get zodiac sign, key dates, and a countdown.

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Due Date

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Current Week

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Baby's Sign

Choose Your Calculation Method

First Day of Last Menstrual Period

Cycle Length

days

Luteal Phase

days

📌 Due date = LMP + 280 days (adjusted for cycle length)

Conception / Ovulation Date

📌 Due date = Conception + 266 days (38 weeks)

IVF Embryo Transfer Date

Embryo Age at Transfer

📌 Due date = Transfer date + (266 − embryo age)

Date of Ultrasound Scan

Gestational Age at Scan

weeks

Days

days

📌 Due date = Ultrasound date + (280 − gestational age in days)

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Estimated Due Date

Enter details above

Your baby's arrival window

🌈 Pregnancy Progress

complete

⏳ Countdown to Due Date

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Weeks

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Days

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Hours

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Mins

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First Trimester

Weeks 1–13

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Second Trimester

Weeks 14–27

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Third Trimester

Weeks 28–40

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How Due Dates Are Calculated

A due date calculator estimates when your baby will arrive based on the length of a typical pregnancy — 40 weeks (280 days) from the first day of your last menstrual period (LMP), or 38 weeks (266 days) from conception. This is known as Naegele's Rule, developed in 1850 and still used worldwide today.

The 4 Calculation Methods

1. LMP Method (Naegele's Rule): Due = LMP + 280 days (adjusted: + cycle_length − 28) 2. Conception Date: Due = Conception + 266 days (38 weeks) LMP = Conception − 14 days (assumed) 3. IVF Transfer: Due = Transfer + (266 − embryo_age) Day 3: + 263 | Day 5: + 261 | Day 6: + 260 4. Ultrasound (Crown-Rump Length): Due = Scan Date + (280 − gestational_age_in_days) Most accurate: first trimester scans (8–14 weeks)

What to Expect Near Your Due Date

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Only 4% Born On Time

Only about 4% of babies are born on their exact due date. About 80% are born within 2 weeks before or after. Due dates are estimates, not appointments.

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Full Term vs Post-Term

Full term is 39–40 weeks. Early term is 37–38 weeks. Late term is 41 weeks. Post-term is 42+ weeks, when induction is typically recommended.

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Ultrasound Accuracy

A first-trimester ultrasound (8–14 weeks) is accurate to ±5–7 days. After 20 weeks, accuracy decreases to ±2–3 weeks. If there's >7-day discrepancy, ultrasound date takes precedence.

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Plan for a Window

Rather than fixating on one date, think of a 5-week window (37–42 weeks). Make practical preparations complete by week 36.

Frequently Asked Questions

Can my due date change after an ultrasound?

Yes. If your first-trimester ultrasound shows a gestational age that differs by more than 7 days from your LMP-calculated due date, your provider may adjust the due date. This is most common in women with irregular cycles. After 20 weeks, providers are less likely to change the due date based on ultrasound measurements, as growth variation increases.

What is a lightning date in pregnancy?

A lightning date (sometimes called a lightening) isn't a date — it's a physical event where the baby "drops" into the pelvis in the final weeks before birth. It can happen 2–4 weeks before labor in first-time mothers and sometimes not until labor itself in subsequent pregnancies. It relieves pressure on the diaphragm but increases bladder pressure.

What happens if I go past my due date?

Going past your due date is common — about 10% of pregnancies reach 42 weeks. Most providers offer membrane sweeping or induction between 40–42 weeks, depending on maternal and fetal health. Biophysical profiles and non-stress tests may be conducted to check fetal wellbeing. Post-term pregnancies (42+ weeks) carry slightly higher risks, so close monitoring is standard.

How are twins' due dates different?

Twin pregnancies typically deliver earlier: dizygotic (fraternal) twins average around 37–38 weeks; monochorionic twins (sharing a placenta) may be delivered at 36–37 weeks due to higher complication risks. The due date is calculated the same way as singleton pregnancies, but most providers and parents should plan for earlier delivery when carrying multiples.

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