Online Tool Store
Pregnancy Due Date Calculator
Estimate a due date, pregnancy week, conception window, and 37-to-42-week arrival range from the last menstrual period and cycle length.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Estimated due date
19 February 2027
About 27 weeks remaining
Pregnancy today
13 weeks, 0 days
Estimated conception
29 May 2026
37 weeks
29 January 2027
42 weeks
5 March 2027
This is an estimate based on a 28-day cycle. A clinician may revise dating using ultrasound and other information.
How to estimate a pregnancy due date
- Enter the first day of the last menstrual period.
- Adjust the average cycle length when it differs from 28 days.
- Review the estimated due date, gestational age, conception estimate, and 37-to-42-week range.
Method and limitations
The estimate uses LMP + 280 days + (cycle length − 28 days). This calendar method assumes ovulation shifts with cycle length and cannot account for every irregular cycle. It supports planning, not diagnosis or clinical pregnancy dating.
Seek advice from a qualified maternity care professional for prenatal care, symptoms, uncertain dates, or decisions based on gestational age.
FAQ
How is the estimated due date calculated?
The calculation starts 280 days, or 40 weeks, after the first day of the last menstrual period, then adjusts by the difference between the entered cycle length and 28 days.
Why does pregnancy dating begin before conception?
Gestational age is conventionally counted from the first day of the last menstrual period. Conception commonly occurs about two weeks later in a 28-day cycle.
Is the due date the exact day labour will begin?
No. It is an estimate used to track pregnancy. Birth commonly happens before or after that date; the displayed 37-to-42-week range provides context.
What if the last-period date is unknown or cycles are irregular?
A last-period calculation may be less reliable. Discuss dating with a midwife, obstetrician, or other qualified maternity care professional.
Can an ultrasound change the estimated due date?
A healthcare professional may use an early ultrasound and clinical information to confirm or revise pregnancy dating when appropriate.
How we compare
| Feature | Online Tool Store | NHS Due Date Calculator | Mayo Clinic |
|---|---|---|---|
| Cycle-length adjustment | Included | Included | LMP estimate |
| 37-to-42-week context | Displayed | Explained | 40-week method |
| Clinical confirmation | Advised | 12-week scan guidance | First-trimester ultrasound guidance |
Use NHS or Mayo Clinic resources for wider pregnancy guidance and follow the due date established by your maternity care professional. Online Tool Store provides a transparent calendar estimate with cycle adjustment and milestone context.