预产期计算器

Use this free pregnancy due date calculator to estimate your due date and current week of pregnancy.
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输入末次月经日期

计算预估预产期和孕期里程碑

预产期是如何估算的

This calculator uses Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period, adjusted for your cycle length. This is the most widely used method for estimating due dates.

Note: Only about 4% of babies are born on their exact due date. Most arrive between 37-42 weeks. Your healthcare provider may adjust the due date based on ultrasound measurements.

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How our pregnancy due date calculator works

1

Enter your last menstrual period

Type the first day of your last period. This is the standard reference date used by most obstetricians.

2

We add 280 days

Naegele's rule: due date = LMP + 280 days (40 weeks). The calculator also shows the date range (38-42 weeks is full term).

3

See week-by-week milestones

Get your current week, trimester, and key dates: first prenatal visit, anatomy scan, viability (24w), and full term (37w).

Key things to know about our pregnancy due date calculator:

  • Due date accuracy: Only 5% of babies arrive on their exact due date. Most come within 2 weeks before or after. Treat the due date as a range, not a deadline.
  • Conception date: If you know your conception date (e.g. from IVF or tracking), add 266 days for an alternate due date. Conception typically occurs 14 days after LMP.
  • First vs subsequent pregnancies: First pregnancies average 40 weeks + 1 day. Subsequent pregnancies average 40 weeks + 0 days, but individual variation is large.

For related calculations, try our pregnancy calculator.

预产期推算（Naegele 公式）