Pregnancy Due Date Calculator
Due-date sketch from LMP or conception — ultrasound dating can override this. Click any i for detail.
Dating
Start from
i
Mode
LMP is the common clinic default. Conception date if you know it precisely. |
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|---|---|
First day of last period
i
LMP
Day 1 of the period before pregnancy. |
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Typical cycle length (days)
i
Cycle
Adjusts the classic +280-day rule when cycles are not 28 days. |
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Conception date
i
Conception
Known conception or transfer date when you are not using LMP. |
How to use this calculator
- Choose LMP or conception dating.
- Enter the matching date (and cycle length for LMP).
- Read the estimated due date, conception sketch, and gestational age today.
- Prefer your obstetric provider’s dating if an early ultrasound disagrees.
Results explained
Naegele’s rule adds 280 days (40 weeks) to LMP for a 28-day cycle. Longer or shorter cycles shift that by (cycle − 28) days. From a known conception date, pregnancy length is about 266 days (38 weeks). Only a fraction of births happen on the exact due date; it is a midpoint for planning, not a guarantee.
Quick reference: pregnancy dating
LMP + 280 days (adjust for cycle) or conception + 266 days.
| Item | Detail |
|---|---|
| 40 weeks | LMP dating convention |
| 38 weeks | From conception / fertilization |
| Cycle 32 days | Due date ~4 days later than classic Naegele |
| Ultrasound | Often preferred in the first trimester if dates conflict |
Not medical advice — confirm dating with your prenatal care team.
How the estimate is built
EDD_LMP = LMP + 280 + (cycle − 28); EDD_conception = conception + 266.
Example scenario
LMP Jan 1, 28-day cycle → due date about Oct 8 the same year.
FAQ
Why does my app disagree by a few days?
Apps may assume a fixed 28-day cycle, different time zones, or ultrasound-adjusted dating. Small gaps are common; ask which method your clinic chart uses.
What about IVF?
Transfer dating often uses embryo age plus days since transfer. This page’s conception mode is a simple +266 sketch — use your clinic’s IVF calendar when you have one.
Is the due date when labor starts?
Only sometimes. It is a statistical midpoint. Full-term windows span weeks, and providers watch maternal and fetal cues more than one printed day.
Can I enter today’s date as LMP?
Only if today truly is day 1 of that period. Wrong LMP is the most common reason DIY due dates look off.