Pregnancy Conception Calculator – When Did Baby Get Conceived?

  • Adam
  • November 1, 2025

Free pregnancy conception calculator. Calculate the likely conception date based on due date, last period, or ultrasound. Find the intercourse window when pregnancy occurred.

✨ 👶 💕

Pregnancy Conception Calculator

Calculate when conception likely occurred based on your due date, last period, or ultrasound date. Discover the range of dates when intercourse may have led to pregnancy.

📋 Quick Navigation

✨ Calculate your conception date! 👶
Your estimated delivery date
First day of your last menstruation
21-35 days
Date of your scan
weeks at scan
Likely Conception Date
TBD
estimated date

Conception Date

—
likely date

Intercourse Window Start

—
earliest date

Intercourse Window End

—
latest date

Window Duration

6
days

📊 Conception Timeline

Event Date Details
Intercourse Window Start — Earliest intercourse date (sperm survives up to 5 days)
Likely Ovulation — Estimated ovulation date
Likely Conception — Most probable conception date
Intercourse Window End — Latest intercourse date (egg survives ~24 hours)
Implantation — Embryo implants in uterus (6-12 days after conception)
Positive Test — hCG hormone detectable
Due Date — Estimated delivery date (40 weeks from LMP)

✨ Understanding Conception

What is Conception?

Conception is when a sperm cell fertilizes an egg cell, creating a new life. This typically occurs during ovulation, when a mature egg is released from the ovary. The fertilized egg then travels down the fallopian tube and implants in the uterus 6-12 days later.

When Does Conception Occur?

Conception typically occurs around day 14 of a 28-day menstrual cycle, during ovulation. However, exact timing varies based on individual cycle length and ovulation variation. Ovulation can occur any day from 7-21 of the cycle, with most occurring around day 12-16.

Sperm vs Egg Survival

Sperm Survival: Sperm can survive in the reproductive tract for 3-5 days, with most viable for 2-3 days. This is why intercourse days before ovulation can still result in pregnancy. Egg Survival: The egg survives for only 12-24 hours after ovulation. This narrow window combined with sperm survival creates the "fertile window."

From Conception to Pregnancy Detection

Day 0-2: Conception occurs, sperm fertilizes egg. Days 3-5: Fertilized egg divides as it travels. Days 6-12: Embryo implants in uterus. Days 10-14: hCG hormone produced and enters bloodstream. Days 12-14: Blood tests detect pregnancy. Days 14+: Home urine tests may detect pregnancy.

💡 Note: Conception date and intercourse date are not the same. Intercourse can occur 5 days before conception if sperm survives. This is important for relationship and paternity considerations.

💕 The Intercourse Conception Window

The Fertile Window

The fertile window (time when pregnancy can occur) is approximately 5-6 days: the 5 days before ovulation and the day of ovulation. This is based on sperm surviving up to 5 days and the egg surviving for 1 day.

Why 5 Days Before Ovulation?

Sperm can survive in the female reproductive tract for up to 5 days in ideal conditions (cervical mucus is favorable during the fertile window). If intercourse occurs 5 days before ovulation, sperm can still fertilize the egg when it's released. This is the biological basis for the fertile window calculation.

Peak Fertility vs Fertile Window

Fertile Window: 5-6 days (when pregnancy can occur). Peak Fertility: 2-3 days before and including ovulation. Most Likely to Conceive: The day before ovulation and ovulation day itself.

Intercourse Timing & Pregnancy Success

Studies show that intercourse on the day of ovulation and the day before have approximately 50% chance of conception. The 3 days before ovulation: 20-40% chance. The 4-5 days before: 5-15% chance. Having intercourse every day during the fertile window maximizes conception chances.

📌 Important: Intercourse should not have occurred exactly on the conception date. The actual intercourse date is typically 1-5 days before the estimated conception date, as sperm needs time to meet and fertilize the egg.

🧮 Calculation Formulas

Conception Date from Due Date

Conception Date = Due Date − 266 days
Or: Conception Date = Due Date − 38 weeks

Example: Due Date = August 9, 2026
Conception = August 9 − 266 days = November 16, 2025

Note: Due date is 40 weeks from LMP, conception is 38 weeks from LMP
So: Due Date − 14 days ≈ Ovulation Date

Conception Date from LMP

Conception Date = LMP + Ovulation Day

For 28-day cycle (ovulation ~day 14):
Conception ≈ LMP + 14 days

For custom cycle:
Conception ≈ LMP + (Cycle Length − 14) days

Example: LMP Nov 2, 28-day cycle
Conception ≈ Nov 2 + 14 = Nov 16

Intercourse Window Calculation

Intercourse Window Start = Conception Date − 5 days
Intercourse Window End = Conception Date + 1 day

Example: Estimated Conception Nov 16
Window Start = Nov 16 − 5 = Nov 11
Window End = Nov 16 + 1 = Nov 17
Possible Intercourse Dates = Nov 11 to Nov 17 (7-day range)

Implantation Date

Implantation Date = Conception Date + 6 to 12 days

Typical implantation: 6-10 days after conception
Range: Nov 22 − Nov 26 (for Nov 16 conception)

Positive Pregnancy Test

Earliest Test: 10-14 days after conception
Most Reliable: 1-2 weeks after conception
Reliable by: Missed period (14 days after conception)

For Nov 16 conception:
Earliest test: Nov 26-30
Most reliable: Nov 30 - Dec 1
By missed period: Dec 1 onwards

❓ Frequently Asked Questions

Can I know the exact conception date? +
No, conception date can only be estimated with accuracy of ±2-3 days. Multiple factors affect exact timing: ovulation variation (±2-3 days), sperm survival (3-5 days), intercourse timing, and individual biology. DNA testing can narrow it to a few days but not pinpoint it exactly.
What if intercourse occurred outside the window shown? +
Pregnancy can still occur if intercourse happened outside the calculated window, but it's less likely. If intercourse occurred 1-2 days after the window end, pregnancy is unlikely but possible. If 6+ days before, pregnancy is extremely unlikely. Ovulation variation and sperm survival are the main variables.
Why is the intercourse window so long (6-7 days)? +
The window accounts for both sperm and egg survival. Sperm survives 3-5 days, egg survives 1 day. Additionally, ovulation timing can vary ±2-3 days. This creates a 6-7 day window when intercourse could potentially result in pregnancy. The wider window accounts for these biological variations.
Does cycle length affect conception date calculation? +
Yes, significantly. For LMP-based calculation, ovulation typically occurs 14 days before the next period. So a 35-day cycle means ovulation around day 21 instead of day 14. This shifts conception date estimate by 7 days. If your cycle varies, the window is larger.
Is this calculator used for paternity purposes? +
This calculator provides estimates only and should not be used as evidence for paternity claims. The wide intercourse window (6-7 days) and ovulation variation mean multiple dates are possible. Paternity determination requires DNA testing. Medical and legal professionals should be consulted for specific cases.
What if I had multiple partners during the intercourse window? +
This calculator cannot determine which partner is the biological father if intercourse occurred during the fertile window. DNA testing is the only way to establish paternity. The calculator shows when conception likely occurred based on medical markers, but not the source of conception.
Does conception date affect how old the baby is? +
Medical age is based on LMP (gestational age), not conception date. So even though baby was conceived at day 14 of pregnancy, doctors count the full 40 weeks from LMP. Fetal age is 2 weeks behind gestational age. Understanding both is important for pregnancy tracking.

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