Pregnancy Due Date Calculator: Accurate Calculation Based on Conception Date

Question
I know my day of conception to be the morning of march 30 2012. My first day of my last period is either the 16 or 17 and it ended before the 25. I've spent time on many different web sites and they all seem to give me a different due date,different ovulation dates, or conception does not jive with the 30 which I know to be the only time I had sex during my ovulation period.(nothing before,during or after my period except on 30,nothing after 30) Also the sites say I'm either 25 weeks and 5 days, or 26 weeks and 6 days and according to my calculations I'm only 25 weeks today(09/14 2012). With my conception being the 30 and most sites saying my due date is DEC 21, 2012, why do I calculate that to be 39 weeks? Now for the real question....I realize sperm can live for 3/5 days  after intercourse, and if an egg is going to be fertilized and conception is going to occur, it will have to happen in a 24 hour period after ovulation. Could my conception day have been on march 31st 2012, or is it more likely to of been the 30, the actual day of intercourse. What would my due date actually be? Thank you     kerrie

Answer
Hello Kerrie,

The problem with online calculators is they all assume that we women have perfect cycles. If the 30th is the only time you had sex during your ovulation period, then it is the time you fell pregnant regardless of what the calculators say. You may have ovulated a little later than their predictions, and that is not unusual.

Based on my calculations, you are just coming into your 26th week. The medical way of calculating it includes some of the days before you conceived, but it has been 25 weeks since you fertilised the egg. This accounts for why you are calculating December 21st as 39 weeks; it's 40 when going by my way of calculating.

As for the precise day of conception, it could just as easily be the 31st as it was the 30th. This depends on the release of your egg, when the sperm met it in the fallopian tubes, and other hormonal factors. The only cases where people really know exact days (rather than one out of two in your case) is when they undergo assisted reproduction techniques. If you did conceive on the 31st, your due date would be December 22nd. However, as less than 5% of babies actually arrive on their due date, it's not something to worry about too much.

I hope you have an enjoyable pregnancy,

Laura