Use the first day of your last menstrual period as the starting date
Count the number of days from that date to today
Divide the total days by 7 to get pregnancy weeks
Count any remaining days as extra days beyond the full weeks
Example: 35 days since last menstrual period equals 5 weeks and 0 days
Example: 40 days since last menstrual period equals 5 weeks and 5 days
If you know the conception date, add 2 weeks to estimate pregnancy weeks
If you have an ultrasound date, use the measurement-based gestational age from that scan
Keep the same method for each weekly update
Ask a healthcare provider if your dates are uncertain or irregular