Pregnancy Conception Calculator
Estimate your conception date based on due date or last menstrual period.
A conception calculator estimates when conception likely occurred based on your due date or last menstrual period.
Examples
Due date of October 8
Frequently Asked Questions
Why is conception date a range and not exact?
Can I determine paternity from the conception date?
Quick Tips
- •Always confirm results with your healthcare provider for the most accurate dating.
- •An early ultrasound (6-9 weeks) provides the most reliable estimate of gestational age and conception timing.
- •If your cycles are irregular, the last menstrual period method will be less accurate — use the due date method instead.
A conception calculator estimates when conception likely occurred based on your due date or last menstrual period.
How to Use This Calculator
Select whether you know your due date or last menstrual period date. Enter the date, and the calculator will estimate the probable conception date range and fertile window.
Understanding the Formula
From due date: Conception = Due Date - 266 days (+/- 2 days). From LMP: Conception = LMP + 14 days (with window of day 11-21 for ovulation variability).
Examples
Due date of October 8
If your due date is October 8, probable conception occurred around January 14-18, with the most likely date being January 16.
Frequently Asked Questions
Why is conception date a range and not exact?
Ovulation timing varies between women and even between cycles. Sperm can also survive up to 5 days inside the body, so intercourse several days before ovulation can result in conception.
Can I determine paternity from the conception date?
While the conception window can narrow down timing, it is not precise enough for paternity determination. DNA testing is the only reliable way to establish paternity.
Assumptions & Limitations
- Based on average cycle lengths; individual cycles may vary.
- Assumes ovulation occurred around day 14 of the cycle, which can differ significantly between individuals.
- Conception date is always an estimate — sperm can survive up to 5 days, making exact dating impossible without ultrasound.