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The conception date calculator works backwards from the estimated due date to estimate when conception occurred. It subtracts 266 days (38 weeks) from the due date, as fertilisation to birth averages 266 days. The last menstrual period is estimated by subtracting 280 days (40 weeks) from the due date.

Formule

Estimated conception = Due date − 266 days

Stapsgewijze handleiding

  1. 1Estimated conception = Due date − 266 days
  2. 2Estimated LMP = Due date − 280 days
  3. 3Gestational age from LMP = 40 weeks; from conception = 38 weeks
  4. 4Conception is typically 2 weeks after LMP in a 28-day cycle

Uitgewerkte voorbeelden

Invoer
Due date: 25 December
Resultaat
Estimated conception: ~1 April (266 days before)
Estimated LMP: ~18 March
Invoer
Due date: 1 June
Resultaat
Estimated conception: ~8 August (prior year)
LMP ≈ 25 July prior year

Veelgestelde vragen

What is Conception Calc?

The conception date calculator works backwards from the estimated due date to estimate when conception occurred. It subtracts 266 days (38 weeks) from the due date, as fertilisation to birth averages 266 days

How accurate is the Conception Calc calculator?

The calculator uses the standard published formula for conception calc. Results are accurate to the precision of the inputs you provide. For financial, medical, or legal decisions, always verify with a qualified professional.

What units does the Conception Calc calculator use?

This calculator works with inches. You can enter values in the units shown — the calculator handles all conversions internally.

What formula does the Conception Calc calculator use?

The core formula is: Estimated conception = Due date − 266 days. Each step in the calculation is shown so you can verify the result manually.

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