The 1%-10% Rule is used to determine the proper level of detail while breaking down the work of a project. The rule states that the lowest level of activities in the WBS of a project should have a duration no less than 1% of the project duration and not more than 10% of the project duration.
For example, if your project will be about 1 year (about 240 business days) long, you have to responsibility to break your project down into as many levels of detail such that activities are:
- Bulleted list item not shorter than 1%
- 240 business days = rounded to 2 business days,
- Bulleted list item not longer than 10%
In a program with multiple levels of management, the 1%-10% Rule can be applied by each level of management: the program manager breaks down the entire program into chunks of work that are not shorter than 1% of the program duration and not longer than 10% of the program duration. For example the program may be expected to last 10 years: the minimum duration for the lowest level items in the program breakdown structure of the program manager is 1%
- 240 business days = rounded to 25 business days or 5 weeks.
The 1%-10% Rule was first published by Eric Uyttewaal in his book "Dynamic Scheduling with Microsoft Project 2000" in the year 2000.
- 10 years = about 5 weeks. Subsequently the program manager identifies the subprojects and assigns the subproject managers. Each subproject manager continues the break down of the program but only within their own subproject applying the 1%-10% Rule again but only to their subproject. If one subproject manager thinks his/her subproject will take about 1 year, the minimum duration for their activities is 2 business days and the maximum duration is 5 weeks.