Pregnancy due date
Naegele’s rule (last period + 280 days) adjusted for your cycle length gives the due date, conception date, trimester boundaries and the 37-week full-term date, plus your current gestational age, progress and countdown when today is supplied.
Runs in your browserEvery computation happens in your browser — your data never leaves this device.
Pregnancy settings
Naegele’s rule: due date = last period + 280 days, adjusted by the difference when the cycle is not 28 days.
Result
Enter the first day of your last period to see the due date and gestational age.
What this tool does
- Just found out you are pregnant? Get the due date first so you can book the early scan, appointments and leave.
- Cycles longer or shorter than 28 days: the adjusted due date fits your own cycle better than the default.
- See how far along you are today (weeks plus days) and how long is left, to line up with the antenatal schedule.
- Look up the dates when the second trimester, third trimester and 37-week full term begin to plan travel and handovers.
Example
Input
Last period 2024-01-01, cycle 28 days, today 2024-05-01
Output
Due date 2024-10-07; estimated conception 2024-01-15; currently 17 weeks 2 days; second trimester; 159 days to go; progress 43.2%; second trimester starts 2024-04-01, third trimester 2024-07-08, full term 2024-09-16
Due date = last period + 280 days + (cycle length − 28).
Frequently asked questions
How is the due date calculated?
With Naegele’s rule: 280 days (40 weeks) from the first day of your last period. If your average cycle is not 28 days the date is shifted by the difference, so a 32-day cycle moves it four days later. The rule assumes ovulation on day 14, so later ovulation pushes the real date back.
Will the baby arrive on the due date?
Usually not — only about 4% of births happen exactly on the due date, and most fall within two weeks either side. From 37 weeks the pregnancy is considered full term and after 42 weeks it is post-term, so clinicians use the confirmed gestational age rather than the due date to make decisions.
Why count from the last period instead of conception?
Because the first day of the last period is far easier to pin down than the ovulation day. Medical gestational age is always counted from that date, so “17 weeks pregnant” is about 15 weeks after conception. This tool uses the same convention as your antenatal notes.
What if the due date disagrees with my ultrasound?
Trust an early ultrasound, especially a crown–rump length measurement before 13 weeks 6 days, which is typically accurate to about ±5 days and more reliable than dates derived from your period. Use this tool for planning and let your clinician confirm the gestational age.
Why do I have to enter “today” separately?
The due date follows from the last period alone, but “how far along am I today” needs the current date. To stay independent of the system clock and time zone, today is an explicit input: the page fills in the current date on load and you can change it to test any date.
Keywords：due date calculatorpregnancy calculatornaegele rulegestational agepregnancy week预产期计算孕周计算怀孕周期末次月经孕期进度受孕日