Conception Calculator

Understand conception timing and fertile windows

Why conception dates are estimates

Conception typically happens near ovulation, but the exact timing varies cycle to cycle. Sperm can survive for several days in fertile cervical mucus, ovulation can shift with stress or sleep changes, and early embryo development rates differ. Thinking in ranges helps reduce anxiety and supports better planning.

Ways to calculate conception

• LMP method: Estimate ovulation as LMP + (cycle length − 14) and set likely conception around the day before to the day of ovulation.
• From EDD (due date): Count back ~266 days for conception and ~280 days for LMP to build a timeline.
• From ultrasound: Use the ultrasound date and the reported gestational age (weeks+days) to derive LMP, then estimate ovulation from your cycle length.
• Known ovulation: If you track ovulation (OPKs/BBT), conception is most likely the day before or the day of ovulation.
• Positive test date: As an educational approximation, assume conception ~10–12 days before a positive result; adjust based on test sensitivity.

How the fertile window works

The fertile window spans the days when intercourse can lead to conception—usually the five days before ovulation plus ovulation day. Likelihood is commonly higher in the two to three days right before ovulation, then drops rapidly afterward.

Ovulation signals to watch

• Cervical mucus: Clear, stretchy “egg‑white” consistency indicates fertile days.
• Basal body temperature: Rises slightly after ovulation, confirming timing in retrospect.
• OPK tests: Luteinizing hormone (LH) surge often precedes ovulation by 24–36 hours.

Practical planning tips

• Track consistently: Record LMP, cycle length, and any OPK positives to refine estimates.
• Plan across a window: Aim for the days before ovulation instead of a single date.
• Recalculate as needed: If your average cycle changes, update the calculator.

Safety and limitations

This global, educational tool does not replace personalized medical advice. Medications, postpartum cycles, and certain conditions may alter timing. For clinical decisions, consult a qualified professional.

Frequently asked questions

• HOW TO estimate conception from my LMP? Enter your LMP and average cycle length. Ovulation ≈ LMP + (cycle length − 14), and conception likely occurs the day before through the day of ovulation.
• HOW TO find conception from my due date (EDD)? Count back ~266 days from EDD for conception. The calculator also derives LMP (~EDD − 280 days) to show your fertile window.
• HOW TO use my ultrasound report? Provide the scan date and weeks+days of gestational age. The tool derives LMP and estimates ovulation based on your cycle length.
• HOW TO narrow my window with OPKs/BBT? Use Known Ovulation. Conception is most likely one day before and on ovulation day.
• HOW TO interpret the doughnut chart? Larger slices represent higher relative likelihood within the fertile window, often peaking in the two to three days before ovulation.