How to Calculate a Due Date With the Woods Method or Nichols Rule

The Woods method, also known as the Nichols Rule, was developed by midwifery professor Carol Wood Nichols. She developed this method for calculating due dates that takes into account the woman's cycle length as well as her previous childbearing activities. This due date is generally more accurate than the standard Naegele's Rule, which is based on 40 weeks. Here is how to calculate your due date by using the Woods Method.

Difficulty: Easy

Instructions

How to Calculate for First-Time Moms

1. Find out the first day of the woman's last menstrual period.

2. Take that date and add 12 months. For example, we'll say the first day of her last menstrual period was October 31, 2008. Adding a year would make it October 31, 2009.

3. Subtract two months and 14 days. This would now make her due date August 17, 2009. If she has a 28-day cycle you are done and this is her estimated due date. If she has a longer or shorter cycle than 28 days, follow the steps below to continue calculating.

4. Adjust for longer cycle length. If her cycle is longer than 28 days you would add those days to her due date. For example, if her cycle is 33 days you would say 33 - 28 = 5. You would now add five days to August 17, which would make her estimated due date August 22, 2009.

5. Adjust for shorter cycle length. If her cycle is shorter than 28 days you would subtract those days from her due date. For example, if her cycle is 24 days you would say 28 - 24 = 4. You would now subtract four days from August 17, which would make her estimated due date August 13, 2009.

How to Calculate for Second-Time or More Moms

6. Find out the first day of the woman's last menstrual period.

7. Take that date and add 12 months. For example, we'll say the first day of her last menstrual period was October 31, 2008. Adding a year would make it October 31, 2009.

8. Subtract two months and 18 days. This would now make her due date August 13, 2009. If she has a 28 day cycle you are done and this is her estimated due date. If she has a longer or shorter cycle than 28 days, follow the steps below to continue calculating.

9. Adjust for longer cycle length. If her cycle is longer than 28 days you would add those days to her due date. For example, if her cycle is 33 days you would say 33 - 28 = 5. You would now add five days to August 13, which would make her estimated due date August 18, 2009.

10. Adjust for shorter cycle length. If her cycle is shorter than 28 days you would subtract those days from her due date. For example, if her cycle is 24 days, you would say 28 - 24 = 4. You would now subtract four days from August 13, which would make her estimated due date August 9, 2009.