Pregnancy Due Date by Conception Date: Calculate with Confidence
Table of Contents
Fast conception-to-due-date math
Add 266 days (38 weeks) to your conception or ovulation date to estimate due date. If you conceived on June 1, your estimated due date is around February 22. Doctors still confirm timing with early ultrasounds because implantation variance can shift the actual gestational age.
Conception vs. LMP dating
Most providers use the first day of your last menstrual period (LMP) plus 280 days. This assumes ovulation on day 14 of a 28-day cycle.
Conception-based dating adds 266 days because gestational age is technically two weeks ahead of conception. If your cycles are longer or shorter than 28 days, conception dating may feel more accurate.
Irregular cycles, ovulation tracking, and fertility tools
Cycle lengths outside 25–35 days benefit from ovulation predictor kits or basal body temperature charts to pinpoint fertile windows.
If you tracked ovulation with LH strips or monitored cervical mucus, use the positive test date or peak fertility day as your conception anchor.
When cycles vary widely, providers often rely on first-trimester ultrasounds (7–10 weeks) for the most accurate dating.
Special scenarios: IVF, FET, and medical oversight
In IVF or ICSI cycles, clinics calculate due dates using embryo transfer day and embryo age (fresh vs. frozen).
Frozen embryo transfers (FET) often use the transfer date plus 266 days, adjusted by embryo development stage (day 3 vs. day 5 blastocyst).
Always confirm dates with your obstetric provider. They will adjust care timelines based on ultrasound measurements and medical history.
Staying informed throughout pregnancy
- Schedule your first prenatal visit as soon as pregnancy is confirmed—early ultrasounds refine due dates.
- Log cycle details and ovulation tracking data in a pregnancy journal or app to discuss with your provider.
- Call your doctor immediately for unusual symptoms such as bleeding, severe cramps, or fever.
Validate dates with your care team
Online calculators provide helpful estimates, but ultrasounds and professional guidance deliver the final word. Bring your conception data to appointments, ask questions, and stay flexible—babies arrive on their schedule even when you track every detail.