预产期计算器
根据末次月经日期（LMP）估算预产期。使用Naegele法则：LMP + 280天。
Overview
An estimated due date is set 280 days — forty weeks — from the first day of the last menstrual period. Naegele's rule reaches the same figure by adding a year, subtracting three months and adding seven days. Dating from a menstrual period rather than from conception means gestational age exceeds embryonic age by about a fortnight throughout the pregnancy.
预估分娩日期
当前周数
w d
剩余天数
妊娠期
预估受孕日
此计算器使用Naegele法则（LMP + 280天），实际分娩日期可能有所不同。请咨询医疗专业人员以获取准确估算。
How to Use
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1
Enter your last period date
Select the first day of your last menstrual period, or switch to conception or IVF-transfer dating.
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2
Confirm the cycle length
Adjust the average cycle length if it differs from the typical 28 days.
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3
Read your due date
Your estimated due date, current week, and trimester timeline are shown instantly.
About
The convention uses an imperfect landmark because it is the observable one: the last period is usually recallable, conception is not. The 280-day standard assumes a 28-day cycle with ovulation on day 14, so a materially longer or shorter cycle shifts the true date by the difference. First-trimester ultrasound measurement dates a pregnancy more precisely and supersedes the calculated value where the two disagree beyond a set tolerance.
Trimester boundaries fall at weeks 13 and 27, viability is conventionally placed near week 24, and term spans weeks 37 to 42. Fewer than one birth in twenty occurs on the estimated date itself.