出産予定日計算機

共有リンク

はじめに

Pregnancy Due Date Calculator — Estimate your due date and current pregnancy week. Enter First day of last period to get an instant, accurate result.

計算式

Naegele's rule: due date = last menstrual period + 280 days (40 weeks).

ステップごとの説明

Enter the First day of last period.
Click Calculate to see your result instantly.

実例

Example: With First day of last period = 2026-10-09, the Pregnancy Due Date Calculator gives Due Date: 2027-07-16, Weeks: 0, Days: 0.

よくある質問

Is this the same method doctors use?

Naegele's rule is the standard baseline estimate, though your doctor may adjust it based on ultrasound dating.

What are the trimester cutoffs?

First trimester: weeks 0–13. Second: weeks 13–27. Third: week 27 onward.

Is this a medical diagnosis?

No. This is an estimate based on average cycle patterns, not a guarantee or a medical diagnosis — actual due dates vary. Always confirm dating and get prenatal care from a doctor or midwife.

What inputs does the Pregnancy Due Date Calculator need?

You'll need to provide: First day of last period. All fields use sensible defaults, so you can see a working example immediately and then adjust the values to match your own numbers.

How accurate is the Pregnancy Due Date Calculator?

The Pregnancy Due Date Calculator applies the formula exactly as calculated — Naegele's rule: due date = last menstrual period + 280 days (40 weeks). — so results are precise for the inputs you provide. Accuracy depends on entering correct, realistic input values.

Is the Pregnancy Due Date Calculator free to use?

Yes, the Pregnancy Due Date Calculator is completely free, requires no signup, and runs instantly in your browser.