Conception Date Calculator

Professional reverse-calculation of conception time: supports precise calculation of the best conception window from due date, last menstrual period (LMP), ovulation day, and ultrasound gestational age. Provides ovulation prediction, fertile window calculation, and intercourse timing guidance to help couples conceive scientifically and improve pregnancy success rate. Also supports IVF conception date reverse-calculation.

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Accurate Conception Date Calculation

Choose a calculation mode, and the system will automatically give the most accurate conception window and intercourse advice

Select your known due date
Used to back-calculate LMP and ovulation
How long sperm survives in the female body
How long the egg survives after ovulation
Affects conception-window calculation
Affects gestational age calculation

How Conception Date Calculation Works

Understand the formula principle, error sources & conception tips in 3 minutes, and calculate with confidence

Common Formulas & Applicable Scenarios
Known Condition Calculation Formula Accuracy Remarks
Due Date Due date - 280 days ★★★★★ Most accurate reverse calculation
LMP LMP + 14 days (28-day cycle) ★★★★☆ Accurate for regular cycles
Ovulation Ovulation day ± 1 day ★★★★★ Confirmed by ovulation test/B-ultrasound
B-Ultrasound Exam date - gestational age ★★★★☆ Early ultrasound more accurate
How is the fertile window determined?
  • Sperm survives in female body 2–7 days (average 3 days)
  • Egg survives after ovulation 12–24 hours (max 48 hours)
  • Best conception timing: intercourse 1–2 days before ovulation
  • Fertile window: 5 days before ovulation to 1 day after

Tips to Improve Accuracy

Use ovulation test strips, basal body temperature, and cervical mucus observation together to confirm ovulation day and improve accuracy.

Cycle length can vary with stress or illness; averaging 3 months gives a better reflection of true ovulation pattern.

Abstinence of 2–7 days yields best sperm quality; too long or too short affects success. Have intercourse every other day during the fertile window.

Special Cases Conception Day Calculation

What if I forgot my LMP?

If you forgot the exact LMP date, you can back-calculate via:

  • Recall when early pregnancy symptoms started (usually week 6)
  • Combine with first fetal movement time (multipara weeks 16–18, primipara weeks 18–20)
  • Refer to early ultrasound results
  • Remember intercourse dates and contraception use
Determining Conception Day for IVF

Calculation for different transfer types:

  • Day-3 embryo transfer: Transfer day + 3 = conception day
  • Day-5 blastocyst transfer: Transfer day + 5 = conception day
  • Frozen embryo transfer: Count according to embryo development days
  • Actual fertilisation occurred during lab culture

Ovulation Detection Methods Comparison

Choose the most suitable ovulation monitoring method to lock in conception timing accurately

Ovulation Test Strip
Accuracy 90-95%
  • ✓ Easy to use, test at home
  • ✓ 24–48 h advance warning
  • ✓ Relatively low cost
  • ✗ Need daily fixed-time testing
  • ✗ Some drugs may interfere
Suitable for: first-time TTC, regular cycles
Basal Body Temperature
Accuracy 80-85%
  • ✓ Very low cost, just a thermometer
  • ✓ Confirms ovulation has occurred
  • ✓ Shows luteal function
  • ✗ Cannot predict ovulation
  • ✗ Requires strict measuring conditions
Suitable for: patient, regular lifestyle
Cervical Mucus
Accuracy 75-80%
  • ✓ Completely free
  • ✓ Can predict several days ahead
  • ✓ Learn your body's changes
  • ✗ Requires experience
  • ✗ Highly subjective
Suitable for: experienced, observant women
B-Ultrasound Monitoring
Accuracy 95-98%
  • ✓ Most accurate method
  • ✓ Can see follicle development
  • ✓ Professional medical guidance
  • ✗ Requires hospital visits
  • ✗ Higher cost
Suitable for: long TTC, need precise monitoring
Professional advice: First-time TTC women are recommended to start with ovulation test strips and verify with BBT. For irregular cycles or long TTC, hospital B-ultrasound monitoring is advised.

Conception Date Calculation FAQ

Not necessarily. Sperm can live 2–7 days in the female body, and the egg 12–24 hours. Conception may occur 1–6 days after intercourse; the best timing is intercourse 1–2 days before ovulation.

Because ovulation is a necessary condition for conception; the egg must be fertilised within 24 hours after release. Ovulation day confirmed by test strips or B-ultrasound can pinpoint the conception window precisely.

Record 3–6 cycles and average, or use ovulation monitoring (test strips, B-ultrasound) to identify ovulation day. For extremely irregular cycles consult a doctor for professional evaluation.

The "conception day" for IVF is the embryo transfer day. Day-3 embryo: transfer + 3 days; Day-5 blastocyst: transfer + 5 days. Actual fertilisation happened during lab culture.

Quite accurate. Normal pregnancy is 280 days (40 weeks) with an error range of ±2 weeks. After early B-ultrasound verification the error can be narrowed to ±3 days, making it a reliable way to back-calculate conception.

Yes. During the fertile window every-other-day intercourse is recommended, ensuring sperm quality while not missing ovulation. Daily intercourse may lower sperm concentration, while intervals >3 days age the sperm.

Accurate conception day helps: 1) precisely calculate due date; 2) assess whether fetal development is normal; 3) determine check-up schedule; 4) provide reference for next conception; 5) satisfy parents' curiosity.

Implantation happens 6–12 days after conception; hCG is secreted 1–2 days later. Blood test can detect as early as 10–12 days after conception, urine test strips usually require 14–16 days for accurate results.

Menstruation may not have returned while breastfeeding; back-calculate via: 1) recall intercourse history; 2) earliest early-pregnancy-symptom time; 3) B-ultrasound embryo size; 4) ovulation test results, etc.

Calculation method is identical to singleton, but note: 1) twins due date is usually 2 weeks earlier; 2) dizygotic twins may be conceived on different days; 3) B-ultrasound gestational age may measure larger.