Estimate your pregnancy due date from your last menstrual period, conception date, or embryo transfer date, while viewing an approximate gestational timeline for planning purposes.
The date estimate is calculated from the entered cycle, last menstrual period, conception date or gestational reference using standard calendar intervals.The estimate applies standard calendar intervals to the selected last-period, conception, due-date or cycle information. Irregular cycles, assisted reproduction, ultrasound dating and clinical findings can change the relevant date.
The due date calculator can determine an expected date of delivery, also known as the estimated date of delivery or EDD. It also generates an estimated gestational age, based on the information provided. The calculation uses the first day of your last menstrual cycle, date of conception, or date of embryo transfer depending on what data is available.
This calculator may provide guidance for planning a pregnancy or discussing appointments, but it cannot be used to predictthe exact date labor will begin.
Variations in the menstrual cycle, uncertain dates, assisted reproductive technology details, and clinical assessments may influence the dating of pregnancy. An estimated due date may be confirmed or revised by a clinician based on a medical history and ultrasound measurements.
Select the dating method that matches the information you know most reliably. Enter dates in the requested month, day, and year format, then review the estimated due date and gestational timeline.
Enter the estimated date of conception or ovulation only when it is known with reasonable confidence. The date of intercourse is not necessarily the conception date because sperm can remain capable of fertilization for several days and ovulation timing can vary.
If pregnancy resulted from in vitro fertilization, enter the exact embryo transfer date and select the correct embryo age when the calculator requests it. A day-3 embryo transfer and a day-5 embryo transfer require different adjustments. Confirm these details with the fertility clinic if necessary.
The date of pregnancy is counted from the first day of the last menstrual period, although conception may occur some 2 weeks later. Thus an average pregnancy lasts for 40 weeks (280 days) from the first day of the last menstrual period. These data are called 'estimate of gestational age' rather than 'fetal age'.
Standard technique: 28-day cycle with ovulation on day 14. When supported, cycle-length adjustment will move the estimated due date later for cycles longer than 28 days and earlier for shorter ones. However, this is still an estimate because ovulation often occurs on a different day to the predicted cycle day.
If conception date is known, the calculator will usually add 266 days or 38 weeks. IVF dating is done from the day of embryo transfer and the length of embryo since fertilization and development are more precisely recorded.
For dating from the last menstrual period, the standard formula is:
Estimated due date = first day of the last menstrual period + 280 days
An equivalent form of Naegele’s rule is:
Estimated due date = first day of the last menstrual period + 1 year − 3 months + 7 days
If cycle length is included, the adjustment may be expressed as:
Adjusted due date = LMP date + 280 days + (cycle length − 28 days)
When the conception date is known:
Estimated due date = conception date + 266 days
Suppose the first day of the last menstrual period was January 1, 2026, and the usual menstrual cycle is 28 days.
The estimated due date is October 8, 2026.
If the usual cycle were 30 days and the calculator adjusted for cycle length, two additional days would be added:
October 8, 2026 + (30 − 28) days = October 10, 2026
This adjusted date still assumes ovulation followed the expected pattern. It should not replace pregnancy dating established by a healthcare professional.
The displayed date is an estimated due date, not an appointment with certainty. Pregnancy timing is commonly expressed in completed weeks and days of gestation. For example, “12 weeks and 3 days” means 12 full weeks have passed and the pregnancy is three days into the next week.
The estimated due date represents the point corresponding to 40 weeks of gestational age under the selected dating method. Birth may occur before or after that date. The result may also be used to estimate the current trimester or important points on a pregnancy timeline, but those dates remain approximate.
If a clinical ultrasound produces a different estimate, do not manually change dates or choose whichever result seems preferable. Healthcare professionals consider ultrasound timing, menstrual history, assisted-conception records, and other clinical information when establishing the due date used for care.
This calculator cannot confirm pregnancy, determine fetal health, identify complications, or predict the exact start of labor. It also cannot determine the precise conception date from an LMP alone. A regular menstrual cycle does not guarantee that ovulation occurred on day 14.
The calculation may be less accurate when the LMP is unknown, bleeding patterns are unusual, cycles are irregular, or the wrong IVF transfer information is entered. It also cannot decide whether a due date should be revised after an ultrasound.
Use the result as an informational estimate. Pregnancy dating and healthcare decisions should be discussed with an obstetrician, midwife, fertility specialist, or another appropriately qualified healthcare professional. Seek prompt medical guidance for significant bleeding, severe pain, fainting, breathing difficulty, or any other serious or concerning symptoms rather than relying on a calculator.
A standard estimated due date is based on 40 weeks, or 280 days, from the first day of the last menstrual period. When calculated from conception, it is approximately 38 weeks, or 266 days.
If a reliable conception date or IVF transfer date is available, the calculator may estimate a due date from that information. When none of these dates is known, a healthcare professional may use ultrasound and clinical information to estimate gestational age.
Not necessarily. Intercourse can occur several days before fertilization, and ovulation may not happen on the expected day. An intercourse date should therefore be treated as an uncertain estimate unless conception timing is documented through fertility treatment.
LMP dating assumes predictable cycle and ovulation timing. Ultrasound dating uses pregnancy measurements and may produce a different estimate. A healthcare professional determines which date should be used based on the timing and quality of the available information.
It can. Irregular cycles make ovulation timing harder to infer from the LMP. Even a calculator that adjusts for average cycle length cannot account for every variation, so clinical dating may be especially useful.
A due date is an estimate rather than an exact prediction. Accuracy depends on the reliability of the entered date, cycle regularity, conception information, and clinical findings. The actual birth date may be earlier or later.
Enter the best available date and the cycle information requested. Use the output for planning, then rely on clinical assessment for medical decisions and official pregnancy dating.
Use the most reliable date available rather than selecting a method because it produces a preferred result. The appropriate input depends on how the pregnancy began and how confidently each date is known.
| Calculation Method | Information Needed | When It May Be Useful | Important Limitation |
|---|---|---|---|
| Last menstrual period | First day of the most recent menstrual period | When the LMP is known and menstrual cycles are reasonably regular | Assumes a predictable relationship between menstruation and ovulation |
| Conception date | Known or carefully estimated conception date | When ovulation or conception timing is documented with reasonable confidence | The date of intercourse does not necessarily equal the conception date |
| IVF embryo transfer | Transfer date and embryo age at transfer | When pregnancy resulted from an assisted-reproduction procedure | Incorrectly selecting a day-3 or day-5 embryo can change the result |
| Clinical dating | Medical history and ultrasound findings | When dates are uncertain, cycles are irregular, or clinical confirmation is needed | Must be interpreted by a qualified healthcare professional |
An LMP-based estimate may not be dependable if the date is unknown, bleeding was unusual, cycles are highly irregular, or pregnancy occurred soon after stopping hormonal contraception. A known IVF transfer date may provide more specific timing for an assisted pregnancy. Otherwise, a healthcare professional can review menstrual history and ultrasound findings to establish the pregnancy date used for prenatal care.
A positive pregnancy-test date should not be entered as the LMP or conception date. Pregnancy tests detect hormonal changes after conception and do not identify the exact day fertilization occurred.
The standard LMP calculation assumes a 28-day menstrual cycle with ovulation around day 14. If the usual cycle is longer, estimated ovulation may occur later, moving the calculated due date forward. If the cycle is shorter, the adjusted date may be earlier.
| Average Cycle Length | Adjustment From the Standard Estimate |
|---|---|
| 26 days | Subtract 2 days |
| 28 days | No adjustment |
| 30 days | Add 2 days |
| 32 days | Add 4 days |
This adjustment assumes ovulation shifts consistently with cycle length. It may not accurately represent pregnancies involving irregular cycles or unexpectedly early or late ovulation.
Consider keeping the following information available when discussing pregnancy dating with a healthcare professional:
Do not change the estimated due date used in prenatal care solely because another calculator provides a different result. Small differences can occur because tools use different inputs, assumptions, or cycle adjustments. The healthcare professional managing the pregnancy can determine which date is most appropriate for clinical planning.