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Pregnancy calculator

Pregnancy Conception Calculator

Estimate a likely conception date or window from due date, LMP or gestational age.

Conception timing is an estimate. Early ultrasound is usually more reliable for dating than cycle recall.

Method

Due-date mode subtracts 266 days. LMP mode adds about 14 days. Gestational-age mode subtracts gestational age from the known date and then adds about 14 days from estimated LMP.

Example

If the estimated due date is October 8, subtracting 266 days gives an estimated conception date around January 15. The likely window is broader because ovulation and dating vary.

Common mistakes

Do not treat the estimate as proof of paternity or exact ovulation date. Early ultrasound dating and clinician review are more appropriate for medical questions.

Limitations

This is not paternity, medical or legal evidence. Cycle length, ovulation timing, implantation and ultrasound dating can shift the estimate.

References

Last reviewed: 2026-05-17

Before relying on this result

Use this calculator together with the formula, assumptions, limitations and examples on the page. If the topic involves health, tax, lending, investment, legal, safety or current-rate decisions, treat the number as an estimate and check the relevant primary source or professional guidance.

Calculator metadata last reviewed: 2026-05-14.