Gestational Age Calculator

Automatically calculate gestational age with simple input

By selecting today's date and the date of your last menstrual period, you can calculate your gestational age.
Click on the input field to display the calendar, then click on the relevant date.
After entering, the calculated gestational age as of today will be displayed automatically.

* Please note that this automatic calculation result does not serve as proof of gestational age.

Scheduled Blood Draw Date (mm/dd/yyyy)

First Day of Last Menstrual Period (mm/dd/yyyy)

Pregnancy

Fetal DNA begins to flow into the mother's blood around the 6th week of pregnancy.
The amount of fetal DNA flowing in the mother's blood continues to increase until the 14th week of pregnancy, and once a certain amount accumulates, it is maintained at that level until birth without further increase.
Also, although there have been cases where prenatal DNA testing was performed before the 7th week of pregnancy, we ask for blood to be drawn from the 7th week of pregnancy onwards.

When counting gestational age, it is important to note that fertilization of the sperm and egg does not actually occur until the 2nd week of pregnancy. Since fertilization occurs in the 3rd week, it is from the 4th week of pregnancy onwards that the fertilized egg implants in the uterus and a commercial hCG pregnancy test can be used.

DNA testing is necessary if there is sexual intercourse with multiple men within 10 days before or after the date of fertilization

Even if the actual birth date is more than a week before or after the expected date of delivery, it is not particularly unusual.
It is said that only about 5% of babies are born on their expected due date.
To accurately calculate the gestational period, it is necessary to measure the size of the fetus at an obstetrics and gynecology clinic.
However, due to large individual differences such as irregular periods, it is very difficult to accurately pinpoint the ovulation date and fertilization date.
Therefore, if there is sexual intercourse with multiple men within one week before or after the fertilization date, it is impossible to confirm the father based on the fertilization date. In such cases, it is necessary to confirm the biological relationship through DNA testing.

Frequently Asked Questions

Q.How is gestational age calculated?

Gestational age is calculated starting from the first day of the last menstrual period as '0 weeks and 0 days.' By dividing the number of days from the first day of the last menstrual period to the current date by 7, the gestational age can be calculated as 'X weeks and Y days.' This tool automatically calculates it just by entering the scheduled blood draw date and the first day of the last menstrual period. However, this calculation result does not serve as medical proof of gestational age (1).

Q.What should be noted when counting gestational age?

At 0-2 weeks of pregnancy, fertilization has not actually occurred. Fertilization occurs in the 3rd week of pregnancy, and it is after the 4th week of pregnancy that the fertilized egg implants in the uterus and a positive reaction is obtained with a commercial hCG pregnancy test. In other words, there is a gap of about 2 weeks between the gestational age and the actual development period of the fetus (1).

Q.From what week of pregnancy is prenatal DNA testing possible?

Fetal DNA begins to flow into the mother's blood from around 6 weeks of pregnancy. The amount of fetal DNA continues to increase until the 14th week of pregnancy, and after that, a certain amount is maintained until birth. To ensure testing accuracy, seeDNA recommends blood drawing from the 7th week of pregnancy onwards. Although testing has been performed at less than 7 weeks of pregnancy, 7 weeks or later is the standard for stable results (2).

Q.Is it possible to identify the father from the date of fertilization?

If there is sexual intercourse with multiple men within 10 days before or after the date of fertilization, it is impossible to identify the father from the date of fertilization alone. Only about 5% of babies are born on their expected due date, and it is not unusual for the actual birth to deviate by a week or more from the expected due date. Due to individual differences such as irregular menstruation, it is difficult to accurately identify the ovulation date and fertilization date, so confirmation by DNA testing is necessary (3).

Q.Does the calculation result of gestational age serve as medical proof?

The calculation result of this tool does not serve as medical proof of gestational age. To accurately determine the gestational age, it is necessary to measure the fetal crown-rump length (CRL) by ultrasound examination (echo) at an obstetrics and gynecology clinic. Ultrasound measurement between 8 and 11 weeks of pregnancy is considered the most accurate (1).