What is the best way to calculate due date and estimate delivery date?

It is really complicated. The simple calculations listed below based on a fixed addition from your last menstrual period or those used by most online calculators are terribly inaccurate. A lot of recent research has indicated a number of other variables to consider. (See the page links, further down this page, listed under Related Links).

This is how to calculate your due day. The due month is: your LMP month + 9. The due date is: your LMP date plus 7. For example, if your LMP was 3/10/95: 3 + 9 = 12 (Dec), 10 + 7 = 17 (17th day). If the added month exceeds 12, then you subtract 12. For example, if you LMP was 6/20/95, the month will be (6 + 9) - 12 = 3 (March), and the date will be 20 + 7 = 27, so your due date will be 3/27/96.

• There are loads of methods and calculators out there but their accuracy is limited.

• I was always taught -3 +7, if your LMP was 10/11 you -3m= 7/11 and add 7d= 7/18.

• You can always use an online due date calculator. See the page links, further down this page, listed under Related Links.

• Maybe I don't get it but what is all the maths above? Why would you do all this if someone else would do it for you?
• Due Date Calculation

Pregnancy, on average, lasts 267 days (38 weeks) from conception. If you positively know your conception date, you can add 267 days to it for your due date. The following formulas can also tell your EDD:

Date of the first day of your last period + 281 days = due date
or
Date of the first day of your last period + 7 days - 3 months = due date
The methods here are based on the average 28-day menstrual cycle.