The only way to truly know the exact date of conception is if you opt for fertility treatment or in vitro fertilization. Even when using a fertility calculator, the conception date you are given will usually be based on the assumption that conception took place two weeks after the start of your previous menstrual cycle. This goes back to ovulation and the rule of thumb that is taking place in the middle of a menstrual cycle, with most calculators basing their numbers on a 28-day cycle.

Keeping track of your ovulation dates will help you determine a more accurate date of conception. This is because conception would occur within 24 hours of that date. The question then becomes how to figure out your ovulation date. You can basically forget about the total length of your menstrual cycle since the second half (luteal phase) of the cycle is generally always 14 days. Therefore, a 29-day cycle would have seen your ovulation day arrive on day 15. In short, take the total number of days on your cycle and subtract 14 to get the exact ovulation date. You can then ascertain the conception date by knowing that it would have occurred on the day of ovulation or the day after.

Conception Calculator – Find out the most fertile days

The menstrual cycle of each woman is different, so a better understanding of her body can increase the likelihood of conception.

Please select the first day of your last menstrual period:


Usual number of days in your cycle:

It’s not uncommon for women to assume that conception took place on the day they had intercourse. In fact, sperm can live inside the body for up to five days. Conception could fall anywhere in that time period, depending upon the ovulation date.

Reverse Due Date Calculator

If you know your due date and want to know the conception date, this calculator is for you. It is called reverse due date Calculator. The conception date is found by subtracting 266 days (38 weeks), from your due date.

Due Date

The first thing to remember here is that pregnancy is considered to be 40 weeks long. It seldom, if ever, lasts exactly 40 weeks, as babies can arrive at any given time. There is no reason to be upset about the baby comes before or after then due date, as little ones seldom arrive right on schedule.

The calculation to arrive at your due date is pretty straightforward. All you need to do is know the first day of your last menstrual period, at which point you can either count ahead 40 weeks, or 280 days, to arrive at your expected due date. Using the first day of your last period is the most accurate way to arrive at this date, but it’s not the only way. If you are unaware of the first day of your last period, you can use your conception date to figure out the due date. Simply count forward 266 days from conception to get your estimated due date.