Due date calculator
Last period, conception or IVF transfer date to due date, current gestational age and milestone table
Input
末次月经按「见红第一天」算（不是结束那天）；不确定日期时按 B 超的核算结果为准。
预产期怎么算：内格勒法则、试管修正与孕周口径
最常用的算法是「末次月经第一天 + 280 天」。这就是内格勒法则（Naegele's rule）：从末次月经第一天（LMP）起算 280 天、也就是 40 周。它的前提是默认月经周期 28 天、第 14 天排卵——因为受精往往发生在末次月经后两周左右，所以按末次月经算比按同房日期算更稳定，也更容易回想准确。如果月经周期明显不是 28 天（比如 35 天一次），排卵会相应后移，实际预产期也会顺延，这种情况医生常会按 B 超结果修正，本页的孕周也会跟着显示差异。
知道受孕日或做了试管婴儿，就要用对应的偏移量。按受孕日或排卵日推算，从那天起加 266 天；试管婴儿按移植日算更准：移植第 3 天胚胎加 263 天，移植第 5 天囊胚加 261 天——这两条正是生殖中心的常用口径，因为胚胎在移植前已经在体外培养了两三天。本页把五种输入方式做成同一套日期运算，无论你从哪个起点输入，都会换算出同一个预产期，并据此给出当前孕周。
孕周从末次月经算起，不是从受精算起。医学上的「怀孕第几周」统一从末次月经第一天开始数，所以受精后的实际发育时间通常比孕周少两周左右；这也是为什么「孕 12 周」听起来比实际受孕时间久。孕周 = 已过天数 ÷ 7 取整，余数就是「几天」——比如 8 周 3 天，表示从起点起过了 59 天。医院有时会按 B 超测量的头臀长或双顶径把孕周修正几天，两者相差几天很常见，不必因为差一两天而紧张。
关于日期计算本身。本页的日期加减全部按日历进位（年、月、日直接运算），不使用「毫秒数加减 86400000」这类做法——后者在历史上实行过夏令时的地区会掉一小时、把日期算回前一天（中国 1986~1991 年就实行过夏令时）。所以即便你输入的是几十年前的日期，本页的结果也不会因为时区规则而漂移。所有运算都在你的浏览器里完成，页面不发起任何网络请求，也不把日期写进网址、cookie 或 localStorage。
FAQ
By Naegele's rule as commonly used: the first day of the last period plus 280 days (40 weeks); counting from conception or ovulation adds 266 days instead. For IVF the transfer date is adjusted: a day-3 embryo plus 263 days, a day-5 blastocyst plus 261 days - those two are the fertility-clinic convention, and the page gives each separately.
It is an estimate from a formula, not medical advice. The real birth time depends on cycle length, ovulation timing and the baby; only about 5 percent of babies arrive exactly on their due date, and anything between 37 and 42 weeks counts as common. Trust your obstetrician's checks and ultrasound results - especially with irregular cycles or an IVF pregnancy, have the doctor confirm the dating.
Gestational age counts from the first day of the last period, while hospitals often correct it by fetal size measured on ultrasound - a difference of a few days is routine. This page only adds and subtracts dates; it neither reads nor replaces any test result. The base date can be edited by hand, which is handy for checking how far along a given prenatal visit fell.
The table lists common time windows for routine checkups and screenings (NT around 11-13 weeks, the anatomy scan around 20-24, the glucose tolerance test around 24-28, weekly visits after 37) purely as scheduling reference. Arrangements differ by region and hospital - follow your own doctor and hospital for what is actually scheduled and when.
Nothing. Dates only take part in arithmetic on your own machine: the page makes no network requests, writes nothing to localStorage, cookies or URL parameters, and reloading clears it.