Stax
Tools

Pregnancy Due Date Calculator

Calculate estimated due date from LMP or conception date.

Calculate from

出産予定日を理解する

妊娠週数別のマイルストーン

重要なご注意

推定出産予定日（EDD）は赤ちゃんの到着が期待される日付——最終月経日から正確に40週後です。これは統計的な中間点であり、精密な予測ではありません。EDDを知ることで、出産前診察のスケジュール管理・産休の準備・妊娠の経過理解に役立ちます。

この計算ツールは情報提供のみを目的としています。正確な妊娠期間の確定と個別の出産前ケアについては、必ず産婦人科医または助産師にご相談ください。月経周期が不規則な場合、妊娠初期の超音波による妊娠週数の確定は最終月経日に基づく計算よりも正確です。

  • 6週目：経腟超音波で心拍が確認可能。
  • 12週目：第1トリメスター終了。頸部透明帯スキャンと早期異常スクリーニング。
  • 18〜20週目：形態スキャン（異常スキャン）——主要な臓器系すべてを確認し、希望があれば性別を確認。
  • 24週目：生存可能限界——この時期以降に生まれた赤ちゃんは集中治療で生存の可能性があります。
  • 28週目：第3トリメスター開始。妊娠糖尿病の糖負荷試験（GTT）。
  • 37週目：Early-term（早期正期産）。赤ちゃんは出産可能な状態ですが、39週まで子宮内にとどまることで恩恵を受けます。

よくある質問

How is the due date calculated from LMP?
The standard method is Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a 28-day cycle with ovulation on day 14. The formula: EDD = LMP + 9 months + 7 days, or simply LMP + 280 days.
How accurate is the calculated due date?
Only about 5% of babies are born on their exact due date. Most births occur within 2 weeks before or after the EDD. An ultrasound scan between 8–14 weeks provides a more accurate dating than LMP, especially if your cycles are irregular. Your doctor may adjust your due date based on the scan.
What are the three trimesters?
1st trimester: weeks 1–12 (LMP to 12 weeks). 2nd trimester: weeks 13–26. 3rd trimester: weeks 27–40. The 1st trimester is the period of highest miscarriage risk and critical organ development. The 2nd is often the most comfortable. The 3rd involves rapid baby growth and preparation for birth.
What does 'full term' mean?
A pregnancy is considered full term between 39 weeks 0 days and 40 weeks 6 days. Early term is 37–38 weeks; late term is 41 weeks; post-term is 42+ weeks. Babies born before 37 weeks are preterm. The safe delivery window (37–42 weeks) is 5 weeks wide, which is why the due date is an estimate, not a deadline.
How is the due date calculated for IVF?
For a Day-3 embryo transfer, add 263 days to the transfer date (LMP is calculated as transfer date minus 17 days). For a Day-5 blastocyst transfer, add 261 days. IVF due dates are more precise since the exact fertilisation date is known.

関連ツール