Estimated Due Date Calculator
Use one of the methods below to estimate your baby’s due date and current gestational age.
How this gestational due date calculator works
A due date calculator estimates when your pregnancy reaches 40 weeks. In obstetrics, pregnancy is usually dated from the first day of your last menstrual period (LMP), not from conception. That means “gestational age” includes roughly two weeks before fertilization.
This tool uses standard clinical formulas:
- LMP method: Due date = LMP + 280 days (adjusted by cycle length).
- Conception method: Due date = conception date + 266 days.
- Ultrasound method: Calculates an estimated LMP from scan age, then adds 280 days.
- IVF method: Uses transfer date and embryo age to estimate due date.
Why due dates are estimates, not guarantees
Even with accurate inputs, your due date is an estimate. Only a small percentage of babies are born on the exact estimated due date. Most births happen within a range around that day, and timing can vary based on cycle irregularity, ovulation differences, genetics, and other maternal-fetal factors.
Healthcare professionals often refine dating after early ultrasound measurements. If your provider gives a date that differs from a calculator estimate, follow your provider’s timeline for prenatal planning.
Which dating method should you choose?
1) Last menstrual period (LMP)
This is the most common starting method. If your cycles are regular, LMP dating is usually reliable early in pregnancy. If your cycles are consistently longer or shorter than 28 days, a cycle-length adjustment can improve the estimate.
2) Known conception date
If ovulation or insemination timing is known precisely, this method can provide a practical estimate. It avoids assumptions about cycle length.
3) Ultrasound dating
Early ultrasound, especially in the first trimester, is often very useful for dating. Enter your scan date and the gestational age reported at that scan to estimate your due date.
4) IVF transfer date
IVF pregnancies are commonly dated from transfer details. Using transfer date plus embryo age gives a consistent and clinically relevant due date estimate.
How to interpret your results
The calculator reports:
- Estimated due date (EDD): The projected 40-week date.
- Estimated gestational age today: How far along the pregnancy is right now.
- Estimated conception date: Approximate fertilization timing.
- Days until due date: Countdown to EDD (or days past due date).
- Trimester: First, second, or third trimester based on gestational age.
Typical pregnancy timeline milestones
Every pregnancy is unique, but these milestones are commonly used in prenatal care:
- 8–12 weeks: Initial prenatal labs and first-trimester review.
- 11–14 weeks: Optional first-trimester screening.
- 18–22 weeks: Anatomy ultrasound.
- 24–28 weeks: Gestational diabetes screening.
- 35–37 weeks: Group B strep testing and birth planning.
- 39–40 weeks: Full-term window near estimated delivery date.
Frequently asked questions
Can my due date change?
Yes. A provider may revise your due date if early ultrasound suggests a different gestational age than LMP dating.
What if I don’t know my exact LMP date?
Use another method if possible (ultrasound, conception, or IVF details). Your clinician can help establish an official pregnancy timeline.
What if I have irregular cycles?
LMP-based estimates can be less precise with irregular cycles. Ultrasound-based dating may be more accurate in those cases.
Important note
This calculator is for educational use and planning purposes only. It does not replace professional medical advice, diagnosis, or treatment. For personalized prenatal care and definitive dating, consult your obstetric provider or midwife.