Knowing how many weeks pregnant you or your loved one is can provide valuable insight on the types of activities that the mother-to-be can do, the developmental stage of the baby and the due date of the baby, according to MayoClinic.com. There are several methods of determining how many weeks pregnant you are, the most common being going to the doctor for an ultrasound and hormonal tests. There is also a way to determine how many weeks pregnant you are without asking the doctor.
Step 1
Write down what the current day is. Use the absolute value of the day in terms of day of the year, not day of the month. A day of the year calendar will be helpful for this (see Resources). For instance, if today is November 2, then that is number is 306.
Step 2
Write down the day your last menstrual period started. The easiest way to do this is by charting the day your menstrual period starts each month so that you always have those days to refer back to. You may have to think back and remember which day it was if you have not been charting it. Again, write this number down as a day of the year number. For instance, if your last menstrual period started July 18, then the day is 199.
Step 3
Subtract the current day of the year from the day of your last menstrual period. Using the examples above, if today is November 2 or day 306, and the last menstrual period started on July 18 or day 199, then subtract 199 from 306. Written mathematically 306 -- 199 = 107 days pregnant.
Step 4
Divide the number of days pregnant by 7 to get the number of weeks in pregnancy. Continuing the example from above: 107 / 7 = 15.3 weeks pregnant.
Tips and Warnings
- Remember to add 1 to the date number if you are calculating in a leap year after February. If your pregnancy is straddled between two calendar years, add 365 to the current date number before subtracting the day of your last menstrual period to get the correct days pregnant number.
- Each pregnancy is different. Always consult with your doctor if you are pregnant, think you are pregnant or thinking about becoming pregnant.
Things You'll Need
- Traditional calendar
- Day of the year calendar
- Calculator
