Gestational Age Calculator
How many weeks along from LMP or by backing up from a due date. Click any i for detail.
Dating
Start from
i
Mode
LMP is the usual clinic default; due date if that is what you have. |
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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 pregnancy length when cycles are not 28 days. |
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Due date
i
Due
EDD from your clinic or app when you are not entering LMP. |
How to use this calculator
- Choose LMP or due-date mode.
- Enter the matching date (and cycle length for LMP).
- Read weeks+days along and the paired due-date sketch.
- Prefer ultrasound dating when your obstetric team says dates conflict.
Results explained
Gestational age traditionally counts from LMP, with a 40-week (280-day) due date for a 28-day cycle. From a known due date, this page subtracts 280 days to sketch pregnancy start, then counts forward to today. Embryo age and IVF dating can differ — use your clinic’s calendar when you have one.
Quick reference: gestational age
GA ≈ days since LMP (or since due − 280), shown as weeks + days.
| Item | Detail |
|---|---|
| 40 weeks | Full-term midpoint by LMP dating |
| Cycle 32 days | Due date ~4 days later than classic Naegele |
| First trimester US | Often preferred if dates disagree |
| IVF | Use transfer dating from your clinic |
Not medical advice — confirm dating with your prenatal care team.
How the estimate is built
From LMP: GA = today − LMP; EDD = LMP + 280 + (cycle − 28). From due: start = due − 280; GA = today − start.
Example scenario
LMP 12 weeks ago → about 12 weeks 0 days today (exact day-of-week dependent).
FAQ
Why does my app disagree?
Apps may lock a 28-day cycle, use ultrasound-adjusted EDD, or different time zones.
Is gestational age the same as fetal age?
Fetal/embryonic age is often ~2 weeks less than gestational age counted from LMP.
What if I only know a conception date?
Use the pregnancy due date calculator’s conception mode, then come back with the EDD.
Can GA be negative?
Only if the start date is in the future — check the entered LMP or due date.