Baby Due Date

Calculate your pregnancy due date

After nine long and exciting months, you will arrive at your pregnancy due date. A due date calculator will help to determine when you will deliver your bundle of joy, and many women enjoy looking forward to that defined date on the calendar. Find out how due date calculators work and how accurate they can be.

When is My Due Date?

Although your pregnancy truly starts at conception, it is nearly impossible to determine when exactly that happened. Instead, doctors will calculate due date from the first day of your last period, which means that you are not actually pregnant during the first two weeks of your 40 week pregnancy. A pregnancy due date calculator takes this information, along with your age and the average length of your cycle, and uses it to give you a relatively accurate due date.

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You will be able to find many due date calculators online, but a due date predictor that simply asks for the date of the first day of your last period will likely be the least accurate model. Due date is calculated from two weeks before ovulation occurred, but many women do not have a 28-day cycle, and therefore will not necessarily ovulate on day 14. A calculator that allows you to adjust for your specific cycle length will probably give you a closer estimate.

About Your Estimated Due Date

Your projected due date is really just an estimate, so don't count on delivering that day. In fact, any pregnancy that spans 37 to 42 weeks is considered full-term, although 40 weeks is the average length. Only 5 percent of women will actually deliver on their due date, and some circumstances will result in either an early or late delivery.

The traditional and accepted method of calculating the due date is based on Nägele's rule, which works on the assumption of a 28-day cycle with ovulation occurring at day 14. Women who have irregular periods or significantly shorter or longer cycles will not get an accurate result from this calculation. And then there are certain circumstances that happen during pregnancy to shift expected dates and processes, such as gestational diabetes, which may lead the doctor to induce labor a few weeks early.

It is generally accepted that women who are expecting their first child tend to have longer pregnancies than those who have given birth before, and some studies have shown that a woman's age and ethnic origin can play a role in determining the length of the gestation period. Pregnancy is full of surprises; although it can be nice to focus on a specific date, try not to get too attached or too impatient – you'll be babyproofing your home before you know it.