HesapHanem

Conception Date Calculator

Estimate your conception date

Result

2026-03-24
2026-03-30 – 2026-04-05
Tuesday

How it is calculated

The tool works backwards from the estimated due date: conception = due date − 266 days. 266 days (38 weeks) is the typical time from conception to birth, which is two weeks shorter than the 40 weeks counted from the last menstrual period. It then adds 6 and 12 days to the conception date to show the window in which implantation is generally expected, and gives the weekday of the conception date. The date must be a valid calendar date in year-month-day form. The result is an estimate, because ovulation timing and pregnancy length differ between people, and the actual conception can fall some days either side.

Worked example

Take a due date of 2026-12-15. Subtracting 266 days gives an estimated conception date of 2026-03-24, a Tuesday. Adding 6 days gives 2026-03-30 and adding 12 days gives 2026-04-05, so the implantation window shown is 2026-03-30 – 2026-04-05.

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Common mistakes

  • Entering the date of the last menstrual period instead of the due date; the tool expects the due date.
  • Treating the result as an exact day: it is a mid-point estimate, and cycles that are not 28 days shift it.
  • Mixing up conception with the start of the pregnancy count, which doctors date from the last period, about two weeks earlier.
  • Using a due date from an early ultrasound and a different one from the period date without deciding which one your doctor uses.
  • Expecting the weekday and the dates to depend on a time zone; they are plain calendar dates.

Sources

About this calculator

This calculator estimates your conception date by working backward from your estimated due date, subtracting 266 days (38 weeks) — the average length of pregnancy counted from conception rather than from the last menstrual period. It also estimates the likely implantation window, typically 6 to 10 days after conception.

Expectant parents use it out of curiosity or to help pin down an approximate conception timeline, and it's sometimes used alongside other dating methods to cross-check an estimated due date. Enter your due date to see the estimated conception date, implantation window, and day of the week. 266 days is the conventional figure; in a study that timed ovulation with daily urine hormone tests (Jukic et al., 2013) the median from ovulation to birth was 268 days, and natural variation spanned about five weeks.

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Comments (1)

  • Editorial team

    The tool subtracts 266 days from the due date and lists days 6 to 12 after that as a second window beside the date. That assumes a due date counted from the last period with ovulation around day 14, so the result is an estimate, not a record of a particular day. If your due date was revised after an ultrasound, enter the revised one. Your doctor can explain how the dating was done. Which due date did you use?

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