Calculation of Gestational Age and Estimated Due Date

After much effort, the expectant mother is fortunately diagnosed with an intrauterine pregnancy. So, how do you calculate gestational age and the baby’s estimated due date? The important basis for these calculations is the “Last Menstrual Period” (LMP).

How to Calculate Based on the Last Menstrual Period:

For Women with Regular Menstrual Cycles:

Use the first day of the most recent menstrual period.
For IVF Procedures:

Artificial Insemination: Subtract 15 days from the date of the last procedure.
D3 Fresh/Frozen Embryo Transfer: Subtract 17 days from the transfer date.
D5 Blastocyst Transfer: Subtract 19 days from the transfer date.
For Women with Irregular Menstrual Cycles:

Usually, the obstetrician will make a determination based on the results of an ultrasound.
How to Calculate Gestational Age and Estimated Due Date:

Gestational Age Calculation:
Divide the number of days from the last menstrual period to today by 7.
Estimated Due Date Calculation:
Subtract 3 months or add 9 months to the month of the last menstrual period (using the Gregorian calendar), and then add 7 days to the day.