Pregnancy Conception Calculator
Explore an approximate conception date from an estimated due date or LMP. This calendar assumption cannot determine the exact day conception occurred.
Calculator arithmetic runs locally in your browser and does not require an API.
The interactive calculator loads here when JavaScript is enabled.
How to use Pregnancy Conception Calculator
Select due-date or LMP mode and enter the corresponding date. Treat the result as the model’s reference date, not evidence of fertilization timing or a reliable conception window.
Formula and method
From estimated due date: conception ≈ due date − 266 calendar days. From LMP: conception ≈ LMP + 14 days. The inferred LMP and due date use the same regular 28-day-cycle model.
Understanding the results
Ovulation timing varies, so a single calendar output cannot establish an exact biological event. There is no cycle-length adjustment, ultrasound input or assisted-reproduction dating mode, and this is not a pregnancy test.
Worked example
Entering LMP February 20, 2024 adds 14 days across leap day to give an approximate conception date of March 5, 2024. The date is an assumption, not confirmation.
Pregnancy and conception dates are estimates. A healthcare professional can provide guidance based on your individual situation.
References
Frequently asked questions
Is the displayed date exact?
No. It is a date implied by a simplified cycle assumption, not a finding about when fertilization occurred.
Does the tool give a reliable conception window?
No. The entered dates alone do not establish a biological confidence interval.
Can I change the cycle length?
No. This calculator uses a fixed 28-day-cycle assumption.