Pregnancy lasts about 266 days from conception to birth. So from a due date, subtracting 266 days gives the most likely conception day; subtracting another 14 days gives the estimated last menstrual period; and the ovulation window sits in the few days around the conception estimate. If you start from your LMP instead, the tool adds 14 days for ovulation and 266 days to the due date — the mirror image of the first method.
从受孕到出生约 266 天。从预产期减去 266 天即最可能的受孕日；再减 14 天得到估算的末次月经；排卵窗口则落在受孕估算日前后几天。如果从末次月经出发，工具加 14 天得排卵日、再加 266 天得预产期——与第一种方法互为镜像。
