Can intercourse two days before ovulation cause pregnancy?

Yes — that is actually one of the highest-probability timings, since sperm survive up to 5 days waiting for the egg.

Why does the calculator say 266 days from conception but 280 from my period?

Pregnancy is officially counted from the LMP. Conception happens ~2 weeks later, leaving 38 weeks (266 days) of true fetal development.

Pregnancy Conception Calculator

Works backwards from an expected due date or forward from the last menstrual period to estimate when conception occurred, including the range of days when intercourse could plausibly have led to it (sperm survive 3–5 days).

#pregnancy conception calculator#when did i conceive#conception date estimator#date of conception#intercourse window

Live calculate

Presets

Calculate Based On

Due DateLast Period

Your Due Date

First Day of Your Last Period

Average Length of Cycles

days

Last Period mode only — ovulation is placed 14 days before your next expected period.

Live mode: results update as you type.

Estimated Conception Date

July 5, 2026

intercourse window Jun 30, 2026 – Jul 6, 2026 · calculated from due date (−266 days)

Conception (most likely): July 5, 2026
Possible intercourse window: Jun 30, 2026 – Jul 6, 2026
Estimated due date: March 28, 2027
Gestational age today: 20w + 0d
Fetal age at conception: 0 weeks — gestational age starts ~2 weeks earlier
Method: Due date − 266 days

Conception timeline

Event	Date
Last menstrual period	Jun 21, 2026
Fertile window opens (sperm viable)	Jun 30, 2026
Estimated conception / ovulation	Jul 5, 2026
Intercourse window closes	Jul 6, 2026
Positive pregnancy test (~2 weeks later)	Jul 19, 2026
Estimated due date (40 weeks)	Mar 28, 2027

Conception cannot be pinned to one day — the egg is viable ~12–24 h and sperm up to 5 days, so any intercourse in this window could be the one.

Ovulation rarely lands exactly on schedule. An early ultrasound is the most reliable way to date conception. Estimates for informational purposes only — not medical advice.

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Formula

Conception = due date − 266 days · or Conception = LMP + cycle length − 14 · Intercourse window = conception − 5 to + 1 day

• From a due date, subtract 266 days (38 weeks of actual fetal development).
• From the last period, place ovulation 14 days before the next expected period (cycle length − 14).
• Add sperm viability: intercourse 5 days before conception (or 1 day after) can still result in pregnancy.

Pro tips

• Only ~10–15% of conceptions land on the calendar-predicted day — treat the window, not the date, as the answer.
• Ovulation pain, LH strips and basal-body-temperature shifts beat any calendar estimate.