Estimate your due date, current gestational age, and pregnancy timeline using your last menstrual period, conception date, or typical menstrual cycle length information when available.
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 Pregnancy Calculator can provide an estimated due date as well as provide a current estimated gestational age and an overall estimated duration of pregnancy based on the first day of your last menstrual period, known conception date, or another known date. This calculator can give an estimated number of weeks pregnant as well as an estimated date for when 40 weeks of pregnancy will have been reached depending on your chosen method. These calculations are planning estimates and can be used as guidance. This calculator cannot verify that you are pregnant, that the pregnancy is healthy, or that you will have a specific date of delivery.
If your cycles vary substantially, you do not remember your last menstrual period, or conception timing is uncertain, treat the result as a preliminary estimate. A healthcare professional may revise pregnancy dating after reviewing clinical information and ultrasound findings.
The Pregnancy Calculator estimates a standard 40-week pregnancy timeline. When the first day of the last menstrual period is used, pregnancy is dated from that day—even though conception usually occurs later. This convention is called gestational age.
For a regular 28-day cycle, the established last-menstrual-period method adds 280 days, or 40 weeks, to the first day of the last menstrual period. This is commonly known as Naegele’s rule. If conception or ovulation timing is used instead, approximately 266 days, or 38 weeks, are added because conception generally occurs about two weeks after the start of the cycle in the standard model.
Cycle-length adjustment can improve the calendar estimate for people whose usual cycle is consistently shorter or longer than 28 days. However, cycle length does not reveal the exact day of ovulation, and biological variation remains possible.
When the first day of the last menstrual period is known, the standard formula is:
Estimated due date = LMP date + 280 days
If the calculator adjusts for cycle length, the formula is:
Adjusted estimated due date = LMP date + 280 days + (usual cycle length − 28 days)
When an estimated conception date is used:
Estimated due date = conception date + 266 days
Current gestational age is calculated as the time elapsed between the LMP date and the selected calculation date. It is normally expressed in completed weeks and additional days, such as 12 weeks and 4 days.
Suppose the first day of the last menstrual period was January 1, 2026, and the usual menstrual cycle is 28 days.
Estimated due date = January 1, 2026 + 280 days = October 8, 2026
Because the cycle is 28 days, no cycle-length adjustment is required. If the usual cycle were 30 days, the calculation would add two more days:
Adjusted estimated due date = October 8, 2026 + (30 − 28) days = October 10, 2026
This example illustrates how a consistent difference in cycle length changes the calendar estimate. It does not mean conception or delivery will occur on an exact predicted day.
Your estimated due date represents the calendar date on which the pregnancy reaches 40 weeks under the selected dating method. It is best understood as a reference point for pregnancy planning and scheduling, not as an appointment for delivery.
Gestational age counts completed weeks and days from the first day of the last menstrual period. For example, a result of 10 weeks and 3 days means that 10 full weeks have elapsed and the pregnancy is in its eleventh week. Gestational age is normally about two weeks greater than fetal or conceptional age under the standard 28-day-cycle assumption.
Approximate trimester divisions are commonly displayed as:
| Pregnancy stage | Approximate gestational period |
|---|---|
| First trimester | Week 1 through the end of week 13 |
| Second trimester | Week 14 through the end of week 27 |
| Third trimester | Week 28 until delivery |
Healthcare systems may define trimester transition points slightly differently. Use the dates provided by your prenatal care team when planning tests, appointments, or medical decisions.
The calculator cannot confirm whether you are pregnant. Pregnancy confirmation requires an appropriate test and, when needed, clinical evaluation. It also cannot determine whether a pregnancy is developing normally, identify multiple pregnancy, assess fetal growth, or diagnose complications.
The calculation assumes that the entered date is accurate and that the selected dating method is appropriate. An LMP-based result can be less accurate when periods are irregular, bleeding was mistaken for a menstrual period, or ovulation occurred earlier or later than expected.
Do not use an estimated due date alone to schedule or delay prenatal testing, medication decisions, travel decisions, or medical care. Pregnancy-related decisions should be based on personalized guidance from an appropriately qualified healthcare professional. Seek prompt medical care for concerning symptoms rather than relying on a calculator result.
Gestational age is calculated from the first day of your last menstrual period to the current date. If your LMP is uncertain or your cycles are irregular, a healthcare professional may use other information to estimate how far along the pregnancy is.
The exact conception date is often unknown, while the first day of the last menstrual period is usually easier to identify. Medical pregnancy dating therefore begins from the LMP, approximately two weeks before conception in the standard cycle model.
It provides a useful calendar estimate when the input date is reliable and cycles are regular. Accuracy may be reduced by uncertain dates, irregular cycles, variable ovulation, recent hormonal changes, or an inappropriate dating method.
Yes. A standard estimate adds 266 days, or 38 weeks, to the conception date. However, a presumed conception date based only on intercourse timing may be uncertain.
It can. A consistently longer cycle may move the LMP-based estimate later, while a consistently shorter cycle may move it earlier. This adjustment still cannot identify the exact ovulation date.
Yes. Ultrasound findings and clinical history may support a different pregnancy-dating estimate. Your healthcare professional will determine whether the official due date should be revised.
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 to you. Different pregnancy dating methods can produce slightly different results because they begin from different reference points.
| Information available | Recommended method | Important consideration |
|---|---|---|
| First day of the last menstrual period | LMP method | Most useful when the date is known and menstrual cycles are reasonably regular. |
| Estimated conception date | Conception-date method | Conception may not occur on the same day as intercourse. |
| Known ovulation date | Ovulation-date method | Home tracking can estimate ovulation but may not identify the exact day. |
| IVF treatment dates | IVF-specific dating | Use the official pregnancy dates supplied by the fertility clinic. |
| Uncertain period or irregular cycles | Clinical pregnancy dating | A healthcare professional may use ultrasound findings and medical history. |
A result of 15 weeks and 4 days means 15 full weeks have been completed and four days have passed since then. The pregnancy is therefore progressing through week 16. This distinction can explain why a calculator, pregnancy app, and healthcare record appear to use different week numbers even when they are based on the same date.
Cycle length is counted from the first day of one menstrual period to the first day of the next. If the calculator allows cycle adjustment, use a typical or average length based on several recent cycles rather than selecting the length of one unusual cycle.
For example, if three recent cycles lasted 29, 30, and 31 days:
Average cycle length = (29 + 30 + 31) ÷ 3 = 30 days
A cycle-length adjustment remains an estimate. It assumes that the timing of ovulation changes in a predictable way, which may not reflect every individual cycle.
An initial estimate may change when more reliable information becomes available. A date entered from memory may be corrected, cycle history may reveal that the standard 28-day assumption was inappropriate, or clinical assessment may support different pregnancy dating.
If a healthcare professional establishes an official estimated due date, use that date for prenatal scheduling and medical decisions. Recalculating with different online inputs can create several possible dates without determining which one is clinically appropriate.
LMP-based calculations may be unreliable when cycles are highly variable, periods are absent, or the bleeding date is uncertain. The calculator can still provide a provisional estimate, but professional pregnancy dating may be needed.
Ovulation can return before regular menstrual periods resume. If pregnancy occurs during breastfeeding and no reliable LMP date is available, a standard menstrual-cycle calculation may not accurately estimate gestational age.
Cycle timing may be temporarily unpredictable after stopping some forms of hormonal contraception. Entering an assumed 28-day cycle does not confirm when ovulation occurred.
Pregnancies resulting from IVF require treatment-specific dating. Embryo-transfer date, embryo age, and egg-retrieval date can affect the calculation. Use an IVF-specific calculator or the due date established by the fertility clinic.
The dating method itself may be similar for twins or other multiple pregnancies, but a general calculator cannot identify a multiple pregnancy or predict its delivery timing. Clinical monitoring is required for individualized information.
A pregnancy calculation does not confirm pregnancy or evaluate symptoms. Take an appropriate pregnancy test and contact a qualified healthcare professional for confirmation and personalized prenatal guidance. Seek prompt medical care for severe pain, heavy bleeding, fainting, breathing difficulty, or any symptom that feels urgent. Do not delay care because a calculator suggests that the pregnancy is at a particular stage.