Calculating Your Due Date: Understanding Pregnancy Length & Conception

Question
If pregnancy lengh is calculated as 40 weeks from the first day of your last period, and since conception usually occurs about 2 weeks after last period begins(read all this on your site), technically that would put my due date as DEC 14 2012,but all the due date calculators on line and my midwife say I'm due DEC 21 2012. My first day of my last period was MARCH 16 2012, and I had unprotected sex with my husband on MARCH 30 2012. Which figures out to be my conception day. Would'nt I be 40 weeks on DEC 14 2012? I'm learning so much helpful information from from your site.          thanks  Kerrie

Answer
Hello Kerrie,

Based on your conception day, I would say that you are due on December 21st as well. That is the result I get from calculating it based on the first day of your LMP, as well as the date of conception. I am wondering if you have calculated your due date using a calendar and counting nine calendar months rather than 40 weeks? That's one of the main reasons a lot of women calculate different due dates to their midwives and online calculators :). Either way, I agree with your midwife, you are due on Dec 21st.

I hope you have a lovely pregnancy,

Laura