週番号計算機
日付から週番号を計算、特定の週番号から日付範囲を逆算します。妊娠週数やプロジェクト管理にも活用できます。
Select the first day of your last period
💡 Pregnancy weeks are calculated from the Last Menstrual Period (LMP), and the due date is LMP + 280 days (40 weeks). Actual delivery dates may vary.
📖 使い方
- Select calculation type (Pregnancy/Project/Reverse)
- Enter the relevant date
- View current week or target week date
- For pregnancy, also see due date and progress
✨ 主な機能
- ✓LMP-based pregnancy week calculation
- ✓Automatic due date calculation (40 weeks/280 days)
- ✓Trimester display (1st/2nd/3rd)
- ✓Project week calculation from start date
- ✓Reverse calculate date for specific week
- ✓Visual progress bar (pregnancy)
📐 計算式
Due Date = LMP + 280 days, Current Week = (Today - Start) ÷ 7 + 1💡 計算原理
- •Pregnancy weeks are calculated from the Last Menstrual Period (LMP).
- •Standard pregnancy duration is 40 weeks (280 days), used to calculate the due date.
- •First trimester (weeks 1-12): Major organs form during this period.
- •Second trimester (weeks 13-26): Rapid growth and movement begins.
- •Third trimester (weeks 27-40): Preparation for delivery.
- •Project weeks start with day 1 of week 1 on the start date.
- •Reverse calculation finds the date (targetWeek-1) × 7 days from start.
❓ よくある質問
Q. What is LMP?
A. LMP stands for Last Menstrual Period, the first day of your last period. It's the basis for calculating pregnancy weeks and due date.
Q. How are pregnancy weeks calculated?
A. Divide the days since LMP by 7. For example, 35 days since LMP means you're in week 5.
Q. Is the due date accurate?
A. The due date is an estimate based on LMP + 280 days. Most deliveries occur within ±2 weeks of the due date.
Q. When is project week 1?
A. The project start date is day 1 of week 1. After 7 days, you enter week 2.
Q. How are trimesters divided?
A. First trimester is weeks 1-12, second is weeks 13-26, third is weeks 27-40. Each has different fetal development characteristics.
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