Conception Date Calculator

Estimate your likely conception date and implantation window from your last period or your due date.

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From Last Period From Due Date

First Day of Your Last Period

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Average Cycle Length (days)

Typically between 21 and 35 days. Count from the first day of one period to the first day of the next.

Luteal Phase Length (days)

The time from ovulation to your next period. 14 days is average if you're unsure.

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Free Conception Date Calculator

This free conception date calculator estimates when you most likely conceived, using either the first day of your last period or your due date. It also shows a likely conception range and an estimated implantation window.

Conception happens on the day of ovulation, so we estimate ovulation as 14 days before your next period. If you start from your due date instead, we work backward using the standard 280-day (40-week) pregnancy length to estimate both your conception date and your last period.

How to Use the Conception Date Calculator

Choose whether to calculate from your last period or your due date.
Enter the requested date, plus your cycle and luteal phase length if using your last period.
Click Calculate Conception Date.
View your estimated conception date, likely conception range, and implantation window.
Use the Print, Share, Copy, or Download buttons to save your results.

Features

Calculate from either your last period or your due date.
Shows a likely conception range, not just a single date.
Estimates your implantation window.
Mobile-friendly with print, share, copy, and download options.

Frequently Asked Questions

How is my conception date calculated?

From your last period, we estimate ovulation (and therefore conception) as 14 days before your next expected period. From your due date, we count back 266 days, which is the standard 280-day pregnancy length minus the roughly 14 days between your last period and ovulation.

Why is there a range instead of one exact date?

Conception can only occur on the day of ovulation or in the few days leading up to it, because sperm can survive in the body for several days while the egg is viable for about 24 hours after release.

What is the implantation window?

Implantation is when the fertilized egg attaches to the lining of the uterus, which typically happens 6 to 10 days after conception.

Can I use this to determine paternity or legal dates?

No. This calculator gives a general estimate for informational purposes only. It should not be used for legal, paternity, or medical determination purposes. Consult your doctor for confirmed dates.

Related Calculators

Want a single estimated ovulation date instead? Try our ovulation calculator. Want a full day-by-day fertility breakdown? Check the fertile window calculator. Already know you're expecting? Use the pregnancy due date calculator.

Last Updated: August 2026