About the Pregnancy Due Date
Enter the first day of your last menstrual period and this due date calculator estimates when your baby is likely to arrive, using the standard 280-day (40-week) rule that clinicians call Naegele's rule. Alongside the due date itself, it shows your estimated conception date, exactly how many weeks and days along you are today, and which trimester you are currently in.
Pregnancy is officially counted from the LMP rather than from conception, which is why the first two weeks of pregnancy pass before conception even occurs — this tool follows the same medical convention, so its week count matches what a midwife or obstetrician would tell you. Your date is processed entirely in your browser and never uploaded, keeping this very personal calculation completely private.
Features
- Due date from your last menstrual period
- Standard 280-day rule used by clinicians
- Estimated conception date shown with the results
- Current week, day and trimester at a glance
- Private — your dates never leave the browser
- Free with no account or app required
How to calculate your due date
- Find the first day of your last menstrual period.
- Select that date in the date picker.
- Read your estimated due date and conception date.
- Check how many weeks along you are and your trimester.
Frequently asked questions
How is the due date calculated?
The calculator adds 280 days — 40 weeks — to the first day of your last menstrual period, following Naegele's rule. This assumes a 28-day cycle with ovulation around day 14, which is also how the estimated conception date (LMP plus 14 days) is derived.
How accurate is an estimated due date?
Only about 4 to 5 percent of babies arrive on their exact due date; most are born within two weeks either side. The date is best understood as the middle of a delivery window. A first-trimester ultrasound usually refines the estimate and may shift it by several days.
What if my cycles are longer, shorter or irregular?
The 280-day rule assumes ovulation on day 14 of a 28-day cycle. Longer cycles typically mean later ovulation and a slightly later true due date, and irregular cycles make LMP dating less reliable altogether. In those cases an early dating ultrasound gives a much better estimate.
When does each trimester begin and end?
Using the convention in this calculator, the first trimester runs from week 0 through week 12, the second from week 13 through week 26, and the third from week 27 until birth. Definitions vary slightly between sources, so your care provider may draw the lines a week differently.
Can I rely on this instead of seeing a doctor?
No — this calculator provides an estimate for planning and curiosity, not medical advice. Only a healthcare provider can confirm a pregnancy, date it accurately with ultrasound, and monitor how it progresses. Book an appointment with a doctor or midwife as early as you can.