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Due Date Calculator (by Ovulation)

Calculate pregnancy timeline based on a positive Ovulation Predictor Kit (OPK) or known ovulation date. Accounts for luteal phase logic.

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About

Using the ovulation date is superior to the Last Menstrual Period (LMP) method for women with irregular cycles, Polycystic Ovary Syndrome (PCOS), or variable follicular phases. While standard calculators assume ovulation on Day 14, real-world data shows ovulation can occur anywhere from Day 10 to Day 25+.

If you use Ovulation Predictor Kits (OPKs) or track Basal Body Temperature (BBT), this tool anchors your 40-week timeline to that specific biological event. This aligns the Estimated Date of Delivery (EDD) with the actual fertilization window, providing a more reliable milestone schedule for early pregnancy tracking.

ovulation opk pregnancy timeline

Formulas

The calculator determines the EDD by adding the standard post-ovulatory gestation period:

EDD = Dateovulation + 266 days

To convert this to the standard "Medical Weeks" (LMP-based scale), the formula back-calculates a theoretical LMP:

LMPtheoretical = Dateovulation − 14 days

Reference Data

PhaseStart PointCalculation Logic
Ovulation (Day 0)Positive OPK / Temp ShiftTimeline Anchor
Implantation Window6 - 10 DPODays Post Ovulation
Positive Pregnancy Test10 - 14 DPOhCG Threshold reached
Clinical 4 Weeks14 DPOExpected Period date (Missed)
Clinical 40 Weeks266 DPOFull Term Delivery

Frequently Asked Questions

Enter the day you got your "Peak" or positive result. Ovulation typically occurs 12 to 36 hours after the LH surge detected by the kit. The calculator adjusts for this window automatically in the timeline.
In a 35-day cycle, ovulation likely happens around Day 21, not Day 14. A standard calculator would put your due date 7 days too early. This tool ignores the cycle length and uses the actual event (ovulation), correcting that 7-day error.
DPO stands for Days Post Ovulation. It is the standard unit of time used by fertility trackers to count down to a pregnancy test or menstruation. 14 DPO is equivalent to "4 Weeks Pregnant" in medical terms.