Use this tool to estimate your conception date, fertile window, and due date. You can calculate from your last menstrual period (LMP) or from a known conception/ovulation date.
Note: This calculator provides estimates only and does not replace clinical dating with your OB/GYN or midwife.
How this conceive and due date calculator works
Pregnancy dating is usually based on standardized timelines. Most due date estimates use one of two starting points:
- Last menstrual period (LMP) — the first day of your last period.
- Conception date — often close to your ovulation date.
Because sperm can survive for several days and ovulation timing can vary, conception is often estimated as a window rather than a single exact day. This tool gives practical date ranges to help with planning prenatal care, appointments, and milestones.
Two ways to estimate your due date
1) If you know your LMP
This is the most common method used in early pregnancy. The standard estimate adds 280 days (40 weeks) to the first day of your LMP. If your cycle is not 28 days, conception timing may shift slightly, which is why this calculator also asks for your average cycle length.
2) If you know conception date
If you are tracking ovulation closely or have a known conception date, due date is commonly estimated by adding 266 days (38 weeks) to conception. This method is often helpful when ovulation timing is clear.
Understanding conception and fertile window
Many people search for a “conception day,” but biologically conception is tied to intercourse timing, ovulation, and fertilization in a short window:
- Sperm may survive up to 5 days in fertile cervical mucus.
- The egg is typically viable for 12–24 hours after ovulation.
- Highest chance of conception is usually in the 1–2 days before ovulation and ovulation day.
That’s why this calculator shows a fertile range around estimated ovulation/conception rather than implying perfect precision.
What your estimated due date means
Your due date is a target point, not a deadline. Many healthy pregnancies deliver between 37 and 42 weeks. A due date helps your provider:
- Schedule bloodwork and ultrasound timing,
- Track fetal growth and development milestones,
- Plan screening windows, and
- Monitor post-term pregnancy if you go past 40 weeks.
Typical pregnancy milestones by week
First trimester (weeks 1–13)
- Pregnancy test often positive around week 4–5.
- Early prenatal visit usually in weeks 6–10.
- Dating ultrasound often performed in the first trimester.
Second trimester (weeks 14–27)
- Nausea often improves for many people.
- Anatomy scan is commonly done around 18–22 weeks.
- Fetal movement may become more obvious.
Third trimester (weeks 28–40)
- More frequent prenatal visits.
- Preparation for labor, birth, and postpartum support.
- Monitoring for full-term timing and signs of labor.
Frequently asked questions
How accurate is an online due date calculator?
It is usually a strong first estimate, but ultrasound—especially in the first trimester—can adjust dating for better accuracy.
What if my cycles are irregular?
If cycles are irregular, LMP-based estimates may be less precise. Entering a known conception date (if available) can help, and your clinician may rely more on ultrasound dating.
Can this be used for IVF pregnancies?
IVF dating is typically calculated from embryo transfer and embryo age. This tool is still useful for general education, but IVF patients should follow clinic-specific dating guidance.
Final note
This conceive and due date calculator is designed for planning and education. For medical decisions, symptoms, bleeding, pain, or uncertainty about dates, contact your obstetric provider promptly.