DUE DATE CALCULATOR
Due date calculator, count down to your new arrival.
Enter the first day of your last menstrual period to estimate the due date, current pregnancy week and how many days are left.
Everything runs locally in your browser
How is this calculated?
The due date follows Naegele’s rule: the first day of the last period plus 280 days (40 weeks). The current pregnancy week is the interval between the reference date and the last period divided by 7. If your cycle is irregular, rely on your doctor’s assessment.
FAQ
Is the due date exact?
Not exactly. Only about 5% of babies are born on the due date, and delivery within two weeks either side is normal. This result is for reference only.
Is my data uploaded?
No. Everything is calculated inside your browser and never leaves your device.
示例与注意事项Example & notes
一个例子A worked example
末次月经 2026-01-01：按内格莱法则加 280 天，预产期约 2026-10-08，同时显示当前孕周与倒计时。Last period 2026-01-01 plus 280 days gives a due date around 2026-10-08, along with the current gestational week and a countdown.
注意事项Things to watch
- 内格莱法则默认 28 天规律周期，周期不规律时误差可达一周以上。Naegele’s rule assumes a regular 28-day cycle; irregular cycles can shift the estimate by over a week.
- 预产期只是估算，实际在前后两周内分娩都属正常。It is an estimate — birth within two weeks either side is normal.
- 最终请以医生结合超声的核算为准，本页不提供医疗建议。Your clinician’s ultrasound-based dating wins; this page gives no medical advice.
相关问答More Q&A
孕周是怎么算的？How is the gestational week counted?
从末次月经第一天起算，比受精时间早约两周，这是医学惯例。From the first day of the last period — about two weeks earlier than conception, per medical convention.
能改周期长度吗？Can I adjust the cycle length?
可以，按你的实际周期长度调整，估算会更贴近个人情况。Yes — entering your own cycle length tailors the estimate.