How do I calculate my pregnancy due date?

Your pregnancy due date is calculated by adding 266 days (38 weeks) to your ovulation and fertilization date or 280 days to the first day of your last menstrual period (LMP). babyMed has the most precise pregnancy calculator. Find out why estimating the correct pregnancy due date is important.

Calculating an accurate due date is an important first step in pregnancy. The calculation of the estimated due date (EDD) is based on the day of the date of ovulation and fertilization. The EDD can be calculated by adding 266 days to the day of ovulation/fertilization. 

The first step is to know the first day of your last menstrual period and the length of your menstrual cycle. Enter the date of the first day of the last menstrual period and your average cycle length. Alternatively, you can also enter the day of ovulation, the weeks and days of the pregnancy on ultrasound, or the IVF egg or embryo transfer date.

The due date calculator will then calculate the exact date the baby will be due, as well as other important events such as the date of implantation, when the baby will start moving and dates for important tests like amniocentesis, ultrasound, or glucose screen.

What is the last menstrual period (LMP)?

The LMP is the date of the first day of your last menstrual period. It is the first day that your last menstrual cycle began. It is the first day that you see bright red blood, not just a little brown spotting. You should keep tack of your LMP each month, either elctonically, online, or at home in a calendar. That is the date you use when entering the LMP.

Am I ovulating?

If you don't know the exact date of ovulation, then use our ovulation calculator to the approximate first day of your last menstrual period in a 28-day cycle. If your cycles are longer or shorter than 28 days, then the day of ovulation may change, and this calculator takes that into consideration when calculating your estimated due date.

You can also use this calculator as a reverse due date calculator to find out when you became pregnant. Just enter your due date and we will calculate the estimated day of conception. In addition, you'll get a range of dates that you may have become pregnant.

How can a conception calculator be used?

Conception calculator uses differ from one woman to the next. If a woman has had unprotected sex with more than one man, she may want to use the conception calculator to give her an idea who the father may be. However, if there is no menstrual cycle between the bouts of unprotected sex, a conception calculator will not effectively reveal paternity. Only a paternity test will reveal the true father of the child in this case.

How accurate is a conception calculator?

There is no way of knowing the exact date of conception unless a woman tracks her cycle and has unprotected intercourse only once per cycle. However, you can make an estimated guess! The conception calculator will give you an estimated date of the probable time when conception occurred. 

Could the conception calculator be wrong?

Yes, a conception calculator can be wrong. Ultrasounds can also be wrong as can home pregnancy tests. There is no perfect system for estimating an exact conception date unless intercourse happened only once between menstrual cycles.

Why does the ultrasound give a different due date from the conception calculator?

A conception calculator uses the first day of the last menstrual cycle to determine the probable date of conception. An ultrasound uses the size of the fetus to estimate gestational age. Ultrasound dating can change throughout pregnancy based on the size of the fetus, but the conception calculator will always offer the same probable date of conception based on the last menstrual cycle and length of the average menstrual cycle.

What is the difference between an online conception calculator and the “wheel” conception calculator that a doctor uses?

There is no difference between the two. The doctor uses the first day of your last menstrual cycle to estimate due date and conception date in much the same way the online conception calculator works.

All results are based on the input, so you need to know the accurate first day of their last menstrual cycle to achieve the best and most reliable results.

References and literature used to create the formulas for the babyMed pregnancy due date calculator