Pregnancy Due Date Calculator
Estimated due date from last period using Naegele's rule, plus gestational age and trimester
100% free. Runs entirely in your browser - your files and data never leave your device and nothing is uploaded to any server.
Default 28 days. Longer cycles move the due date later by the extra days. Ultrasound dating from a clinic can differ by a few days and is preferred when you have it.
Most births fall in a window around this date, not on the exact day. Full term is usually from 37 weeks.
Estimates only. Not medical advice and not a diagnosis. Talk to a clinician about your own numbers. This is not antenatal care.
About this tool
Naegele's rule dates pregnancy from the first day of the last menstrual period: 280 days for a 28-day cycle. Longer cycles add the extra days; shorter cycles subtract them. Gestational age on this page is weeks and days from that last period, which is how most clinics write it, not from the day you think you conceived. Conception is estimated as cycle length minus 14 days after the last period. An early ultrasound can shift the due date. Most babies arrive in a window around the estimate, not on the printed day. Estimates only. Not medical advice, not a diagnosis, and not antenatal care.
How to use this tool
- Enter the first day of your last periodThe first day of bleeding, not the day you think you conceived and not a spotting day mid-cycle unless that is what your clinician uses.
- Set cycle length if it is not 28 daysA 32-day cycle moves the due date about four days later. The usual range here is 21 to 45 days.
- Read due date, trimester and days remainingGestational age is counted from last period. Full term on this page is marked from 37 weeks (14 days before the due date).
Key features
- Naegele-style dating with a cycle-length adjustment, not a fixed 40 weeks for every cycle.
- Gestational age in weeks and days, plus trimester 1, 2 or 3.
- Estimated conception date and days remaining.
- Runs in your browser. Dates stay on your device.
Common uses
- A first calendar date before the booking scan.
- Checking trimester when a form asks for gestational age.
- Explaining why a 32-day cycle does not share a 28-day due date.
- Planning leave around a window, not a single guaranteed day.
Tips for better results
- Write down the first day of bleeding when it happens. Memory a month later is often off by a few days.
- If you have IVF or a known ovulation date, a clinic dates from that instead of last period.
- Treat the due date as the middle of a window. Most births are not on the exact day.
- Use a dating scan when you have one. Ultrasound can override Naegele's rule.
Mistakes to avoid
- Entering ovulation or a positive test date as last period. That shifts the due date by about two weeks.
- Ignoring cycle length when your cycles are regularly longer or shorter than 28 days.
- Treating this page as antenatal care, a scan, or a reason to skip a midwife or obstetrician.
- Panicking if you pass the date. Due dates are estimates; many pregnancies continue a few days past them.
Frequently asked questions
Last period plus 280 days, adjusted by (cycle length minus 28). That is Naegele's rule in day form. A 28-day cycle from 1 January 2026 is due 8 October 2026.
Conception is usually about 14 days before a 28-day cycle would predict from last period. If you have IVF or a known ovulation date, ask the clinic which date they filed.
This tool treats trimester 1 as under 14 weeks, trimester 2 as 14 to 27 weeks, and trimester 3 from 28 weeks, counting from last period (98 and 196 gestational days).
No. Dating scans and a midwife or obstetrician remain the source of care. This is a planning calendar.
The page marks 14 days before the due date, which is 37 weeks from last period on a 28-day cycle. Your clinician's definition of early term and full term may be more precise.
Yes. It is free for normal use with no account required, and ToolBox does not add a watermark to your result.
People also search for
- pregnancy calculator
- when is my baby due
- gestational age calculator
- due date from last period
- naegele rule calculator
- how many weeks pregnant
- trimester calculator