Health
Conception Calculator
Last updated: June 18, 2026
A conception calculator is a family planning tool that estimates the approximate date when fertilization occurred. Because the exact moment of conception is difficult to pinpoint, it is standard clinical practice to estimate conception as approximately fourteen days after the first day of the last menstrual period (LMP) for a standard twenty-eight day cycle. Alternatively, if the estimated due date is known, conception is calculated as two hundred sixty-six days prior to that due date. Expecting parents use this tool to trace milestones, understand gestational age, and determine when pregnancy began.
Calculate your estimated conception date and range by entering either the first day of your last menstrual period (LMP) or your estimated due date.
Quick Answer
Calculate your estimated conception date. Enter either the first day of your last menstrual period (LMP) or your estimated due date to see your conception timeline.
Calculation Method
The date your last menstrual cycle began.
Standard Assumptions
- LMP mode assumes a 28-day cycle with ovulation on day 14.
- Due Date mode assumes a standard 266-day gestation from fertilization to delivery.
- Ultrasound dating is generally more precise than date-based estimates.
Estimated Conception Date
Tue, Jun 2, 2026
Window: Sat, May 30, 2026 – Fri, Jun 5, 2026
Estimate only, not medical advice. Conception dates are approximate and depend on individual cycle lengths and biological variability.
Examples
LMP Date · Oct 12, 2025
Conception: Oct 26, 2025 · Due Date: Jul 19, 2026
Due Date · Aug 15, 2026
Conception: Nov 22, 2025 · LMP: Nov 8, 2025
How it works
Conception Calculations & Timeline
Since the exact moment of fertilization is rarely known, clinicians use standardized timelines to track gestational age and calculate milestones:
In a typical 28-day cycle, ovulation and conception happen approximately 14 days after the first day of the last period:
Estimated Conception = LMP + 14 days
Estimated Due Date = LMP + 280 days (40 weeks)
Standard human pregnancy lasts approximately 266 days (38 weeks) from conception, or 280 days from LMP:
Estimated Conception = Due Date − 266 days
Estimated LMP = Due Date − 280 days
The Conception Window
Conception doesn't always happen on the day of intercourse. Sperm can live up to five days inside the body, meaning intercourse that occurred several days prior to ovulation can lead to conception. The estimated conception date represents the day of ovulation and fertilization, but the intercourse that led to it could have occurred within a 5-day window beforehand.
Disclaimer: This calculator is for informational purposes only and does not constitute medical advice. Pregnancy lengths and cycle patterns vary between individuals. Always consult with a qualified healthcare provider for clinical dating and prenatal care.
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Frequently asked questions
It works by calculating backwards or forwards from known pregnancy dates. From the first day of your Last Menstrual Period (LMP), conception is estimated to occur approximately 14 days later. From a known Due Date, conception is estimated to have occurred 266 days prior.
The conception window is the span of days when fertilization was most likely. Because sperm can survive in the female reproductive tract for up to 5 days, and an egg is viable for about 12-24 hours after ovulation, conception typically happens within a 3-to-5-day window surrounding the ovulation date.
It is very difficult to pinpoint the exact day of conception unless you tracked ovulation closely (using temperature or hormone kits) or underwent IVF. This calculator provides an estimate with a standard ±3-day window.
It assumes a regular 28-day cycle with ovulation occurring exactly on day 14. If your cycle is shorter or longer, or if your ovulation dates vary, the estimated conception date will shift accordingly.
For IVF, the conception date is based on the embryo transfer date. For a 3-day embryo transfer, conception is estimated as transfer date minus 3 days. For a 5-day transfer, it is transfer date minus 5 days.
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