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Pregnancy Due Date Calculator

When is your estimated due date (EDD)? Enter how many days ago your last period started and instantly get your current week of pregnancy, trimester, and how many days remain until your due date.

✓ 監修 Julian Bronski · 更新 2026年6月

入力項目

Days since last period 42

days

0280+

Cycle length 28

days

2135+

計算結果

Week of pregnancy (gestational)

–

Days remaining until due date

–

Trimester

–

Estimated conception (days ago)

–

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Pregnancy Due Date Calculatorのしくみ

The calculation uses Naegele's Rule, the medical standard since 1812: the estimated due date (EDD) is 280 days (40 weeks) after the first day of your last menstrual period (LMP). If your cycle length differs from 28 days, the difference is added or subtracted.

Formula: EDD = LMP + 280 + (cycle length − 28) days. Gestational age is counted from day 1 of your last period: week = ⌊days since LMP ÷ 7⌋ + 1. Trimesters: weeks 1–13 = first trimester, weeks 14–27 = second trimester, week 28+ = third trimester.

よくある質問

How accurate is the estimated due date? ▾

Only about 5% of babies are born on their exact due date. A window of ± 2 weeks (weeks 38–42) is considered a normal birth range. An ultrasound between weeks 11–14 (dating scan) provides the most accurate individual estimate.

When does each trimester start? ▾

The first trimester covers weeks 1–13 (organ formation, higher miscarriage risk). The second trimester (weeks 14–27) is generally the most comfortable phase. The third trimester begins at week 28 and ends with delivery around week 40.

What is gestational age vs. fetal age? ▾

Gestational age (used by doctors and shown here) counts from the first day of your last period – about 2 weeks before conception. Fetal age (conceptional age) counts from actual fertilisation. If gestational age is 10 weeks, fetal age is approximately 8 weeks.

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Pregnancy Due Date Calculatorのしくみ

よくある質問

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