When Did I Conceive?

You conceive on the day you ovulate. Use our conception date widget to calculate your day of ovulation and therefore the day you conceived. The calculator is simple and easy to use but is only an estimation of when you got pregnant.

Estimating the Day You Conceived

Because the egg can only survive up to 24 hours after ovulation, you have that window of one day to conceive. You might just want to preserve a record of the date you conceived, or you might be concerned about having taken medicine or drank alcohol around the time of your conception.

Whatever your reason, the following facts will help you understand how to estimate your day of ovulation and conception:

  • The day of your menstrual cycle on which you ovulate depends on the length of your cycles.
  • No matter which day in the cycle you ovulate, you get your period 12 to 14 days later - a 12-14 luteal phase. For example:
    • For the average 28 day cycle, you can ovulate anywhere from days 12 to 14.
    • If your cycles are 34 days long, you will ovulate around days 20 to 22.
  • By counting back 12 to 14 days from the day you expected your next period, you will find the days you most likely ovulated and conceived.

The Length of the Luteal Phase

The length of the first half of your menstrual cycle before ovulation (the follicular phase) will vary if the length of your cycles vary. However, whether your follicular phase is long or short, what remains fairly regimented and predictable is the 12 to 14 day luteal phase after ovulation.

This happens because the lifespan of the normal after-ovulation follicle (the corpus luteum) is about 12 to 14 days after the day you ovulate. The death of the corpus luteum in 12 to 14 days, and the fall in its major hormone, progesterone, is what triggers your uterus to bleed. This is the onset of your next period.

Using the Widget to Make the Calculation

The conception widget uses this science of the menstrual cycle to estimate the date you got pregnant. To simplify the calculation, the widget assumes a 14 day luteal phase, rather than 12 to 14 days. To make your calculation:

  1. In the first box, select the average length of your menstrual cycles from the drop-down list.
  2. In the next three boxes, select the month, day, and year of the first day of your last period.
  3. Click the "Calculate" button.
  4. The widget then displays the estimated date of conception.
  5. You can delete your results and start over by clicking the "Reset" button.

The widget calculates the expected date of your next period and subtracts 14 days to arrive at your estimated date of ovulation and, therefore, conception.

Cycle Lengths and the Widget

If you keep track of your menstrual cycles and they are regular in length and between 24 and 38 days, you can use the widget to find when you most likely ovulated and got pregnant.

However, if your cycles are irregular, it is difficult or impossible to estimate when your next period will be, or would have been if you did not get pregnant. In that case, using this widget or any other calculation to estimate ovulation and conception is unreliable.

The Calculation Is Only an Estimate

Note that any manual or digital calculation can only estimate when you conceived. Except for in-vitro fertilization (IVF), no method of calculating ovulation/conception can pin down the actual day fertilization occurred. If you have doubts about the gestational age of your pregnancy, your doctor can order an early dating ultrasound.

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When Did I Conceive?