Educational tool only. Always confirm dates with your OB-GYN or midwife, especially if ultrasound dating differs.
How this conceive due date calculator works
This calculator estimates your baby's due date using your known conception date (or IVF transfer date). In a typical pregnancy, the estimated due date is 266 days (38 weeks) after conception. That matches the standard obstetric model of 280 days from the first day of the last menstrual period (LMP), because ovulation and conception usually happen about 14 days after LMP.
If you conceived naturally and know your ovulation date, this method can be very useful. If you conceived through IVF, the calculator adjusts your due date based on embryo age at transfer.
What you get from the result
- Estimated due date in a readable calendar format.
- Estimated LMP date based on conception timing.
- Current pregnancy age in weeks and days (gestational age).
- Days remaining until due date (or days past due).
- Milestones like 12 weeks, anatomy scan period, and full-term start.
Conception date vs. LMP dating
Conception-based dating
Uses the actual fertilization window. Formula: Conception date + 266 days.
LMP-based dating
Most clinics use LMP at first, then adjust if early ultrasound suggests a different gestational age. Formula: LMP + 280 days.
Why ultrasound may change your due date
First-trimester ultrasound is often the most accurate clinical dating method. If there is a meaningful difference between your calculated date and ultrasound measurements, your provider may revise your estimated due date.
Important notes about due date accuracy
A due date is an estimate, not a guarantee. Most births happen within a range around the due date. Many healthy pregnancies deliver anywhere from 37 to 42 weeks, with spontaneous labor often occurring before or after the exact estimated day.
- Only a small percentage of babies are born on the exact due date.
- Cycle irregularity can shift ovulation timing in natural conception.
- Implantation timing and embryo development vary by pregnancy.
- Clinical context (ultrasound, maternal history, multiples) always matters.
IVF due date calculations
IVF pregnancies are often easier to date precisely because transfer timing is known:
- 5-day embryo transfer: transfer date + 261 days
- 3-day embryo transfer: transfer date + 263 days
This calculator applies those formulas automatically when you choose the IVF option.
Frequently asked questions
Can I use ovulation date instead of conception date?
Yes. For practical purposes, ovulation date and conception date are close enough for due-date estimation.
Is this a medical diagnosis?
No. It is a planning tool. Use it for a quick estimate, then follow your provider's official dating.
What if my date from this tool and my ultrasound date don't match?
Follow your clinician's guidance. Early ultrasound is often prioritized for official pregnancy dating.