Pregnancy Due Date Calculator
How to calculate your due date
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Your estimated due date comes from Naegele’s rule, a standardized calculation in which 280 days are added to the first date of your last menstrual period. It’s not at all specific to you or your body, and there’s a lot of variability. However, it gives you and your obstetrician an idea of generally what to expect regarding the timeline of your pregnancy.
An estimated due date (EDD) serves as a guideline for monitoring fetal development and planning prenatal care.
Jump to insightThe standard calculation method adds 280 days to the first day of your last menstrual period, but variations exist for those who conceived through in vitro fertilization or have different cycle lengths.
Jump to insightOvulation timing varies, but conception typically occurs within 12 to 24 hours after ovulation. Tracking ovulation through basal body temperature or predictor kits can help, but an ultrasound is often the most reliable method for pinpointing conception.
Jump to insightWhat is an estimated due date?
An estimated due date (EDD) is the approximate date when a pregnant individual is expected to give birth. It is calculated based on either the first day of the last menstrual period (LMP) or the known date of conception. While the EDD provides a general timeframe for delivery, a small percentage of births occur exactly on this date. Most births happen within a two-week window before or after the estimated due date. Medical professionals use this estimation to monitor fetal development, plan prenatal care and prepare for delivery.
How to calculate your due date
To calculate an estimated due date, follow these steps:
- Determine your date of conception. This date is between 12 and 24 hours after the date of your last ovulation. Unless you’ve undergone in vitro fertilization, the calculation is likely to be imprecise.
- From this date, add 280 days (or nine months and seven days). That’s your estimated due date.
- If you’ve conceived through in vitro fertilization (factoring in the number of days your embryo has grown prior to your embryo transfer) or know the precise date of conception, instead of 280 days, add 266 days to that date. That’s your estimated due date.
If you haven’t been tracking your ovulation or aren’t sure of the date of conception, there’s another method to calculate your due date based on your last menstrual period.
To calculate using your last menstrual period, follow these steps:
- Determine the first day of your last menstrual period.
- Count back three months from that date (and be mindful of which months have 28 or 31 days).
- Add 372 days (one year and seven days) to that date. That’s your estimated due date.
| Conception month | Birth month |
|---|---|
| January | October |
| February | November |
| March | December |
| April | January |
| May | February |
| June | March |
| July | April |
| August | May |
| September | June |
| October | July |
| November | August |
| December | September |
Determining your conception date
Determining your conception date can be tricky, as sperm can survive in the reproductive tract for up to five days, and ovulation timing can vary. Typically, conception occurs within 12 to 24 hours after ovulation. If you have been tracking ovulation using basal body temperature or ovulation predictor kits, you may have a clearer idea of your conception date. Otherwise, if you are unsure, an obstetrician can help estimate it based on ultrasounds and cycle history.
If you do not remember the date of your last menstrual period (LMP), an early ultrasound can provide an estimated conception date. Ultrasounds can detect pregnancy as early as four weeks after LMP, but an embryo may not be visible until about five weeks. If you have a longer cycle but it remains predictable, you can adjust Naegele’s rule to fit your cycle length for a more accurate estimate.
For those with irregular menstrual cycles, pinpointing the conception date can be more complex. In such cases, an ultrasound remains the most reliable way to estimate conception and the due date. Since cycle length and ovulation timing vary widely, it is best to consult a healthcare provider for the most accurate assessment.
FAQ
Can my due date change?
Yes. The dates you provide, the number of embryos you’re gestating and your genetic heritage can be a factor in determining the estimated due date.
Why do due dates change?
A due date change is unlikely if you have regular 28-day menstrual cycles but more common if you have an irregular cycle. Your due date will be affected by probably no more than a week or two, but other factors may elongate your pregnancy, including your birth history and your family’s birth history.
When can I take a pregnancy test?
A pregnancy test can typically detect pregnancy as early as 10 to 14 days after ovulation, though accuracy increases after a missed period. Home pregnancy tests measure human chorionic gonadotropin (hCG) levels in urine, which rise rapidly in early pregnancy. For the most accurate results, take a test first thing in the morning when hCG levels are most concentrated. If you receive a negative result but still suspect pregnancy, wait a few days and test again, or consult a healthcare provider for a blood test, which can detect lower levels of hCG earlier than urine tests.
Will I give birth on my due date?
The odds of giving birth on your due date are very low. No pregnancy is likely to result in birth on an on-time due date. If your baby arrives on a date you and your obstetrician expect, it may be the result of improved technology, or your baby’s birth date may be the result of a planned induction or C-section.
How do twins or multiples affect due dates?
If you’re having twins or a higher-order gestation, your largest embryo will determine the estimated due date.
