Due Date Calculator

Pregnancy dating estimates the end of a 40 week pregnancy. The most common method starts with the first day of your last menstrual period, then adds 280 days. That method assumes ovulation happened about 14 days after bleeding started. If your cycle is longer or shorter than 28 days, the estimate may move by a few days. This calculator uses your period date and cycle length as the starting point. If you know ovulation or conception timing, an estimate based on either date may fit better.

To calculate due date from your last period, start with the first day of your last menstrual period and add 280 days, or 40 weeks. For example, if your last period started on January 1, the estimated due date would be around October 8 in a non-leap year. This is called LMP dating, and an LMP-based estimate uses the same rule. If your cycles are longer than 28 days, ovulation may happen later, so the result may need a small adjustment.

This calculator gives an estimate, not a fixed delivery day. For regular 28 day cycles, the result can be useful for early planning, but many babies arrive before or after the estimated date. First trimester ultrasound is often used to confirm dating because early fetal size follows a predictable pattern. Use the result for planning, then let your doctor confirm the clinical estimate.

Yes. Conception-based dating usually adds 266 days to conception. This can work if you know the likely conception timing from tracking, treatment, or one clear window. It is less certain if sex happened on several days in the fertile window, because sperm can live up to 5 days and the egg usually lives 12 to 24 hours. If you are still estimating conception from cycle timing, compare this estimate with our fertility calculator to narrow the window.

Ovulation-based dating estimates the due date by adding about 266 days to ovulation day. This can be useful for people with longer cycles, shorter cycles, or ovulation test data. For example, if ovulation was on January 15, the estimated due date would be around October 8. That method often fits better than LMP dating when ovulation did not happen on cycle day 14. If you do not know ovulation day, use the cycle length in this calculator first, then check the ovulation estimate.

The due date is the estimated day a pregnancy reaches 40 weeks of gestational age. Gestational age describes how far along the pregnancy is now, counted in weeks and days from an actual or equivalent last-period date. This calculator shows both values and places trimester and term milestones on the same dating timeline.

This tool can still give a rough estimate with irregular periods, but the margin of error is wider. If cycles vary by more than 7 days, ovulation may also shift by a week or more. In that case, LMP dating can be off. Enter your best average cycle length in the calculator, then talk with your doctor about ultrasound dating. Early ultrasound, often in the first trimester, can help confirm gestational age when period dates are unclear.

Yes. Our conception calculator starts with an estimated due date and works backward to estimate fertilization timing, a possible intercourse window, and an equivalent last-period date. Because the due date is an estimate, the dates calculated from it are estimates too.

Yes. IVF dating uses embryo transfer timing and embryo age, not the usual LMP rule. A day 5 embryo transfer often uses transfer timing plus 261 days. A day 3 transfer often uses transfer timing plus 263 days. That is why an IVF-specific calculator is better for IVF, FET, donor egg, and embryo transfer cycles. This tool is meant for last period, ovulation, conception, or ultrasound-based estimates. For treatment cycles, use an IVF-specific tool or follow your clinic's date.

Call an obstetric provider after a positive pregnancy test to ask when they want your first visit. Many offices schedule an early visit around 6 to 10 weeks, depending on history, symptoms, and local practice. The result can help you explain your LMP timing and estimated pregnancy week. Seek urgent care sooner for heavy bleeding, severe one-sided pain, fainting, fever, or shoulder pain. Online dating tools are for planning, not diagnosis.