Lessons · Project management · the 100% rule
The 100% rule: the children add up to the parent, exactly
Every level of the WBS contains all of the work of the level above and nothing more; the children of any box sum to exactly that box.
Hone is a place to practise a career, one idea a day. This is one of its lessons, written out in full and free to read without an account.
What it is for
The budget rolls up from the work packages, so a package left out of the WBS is money left out of the budget, and it surfaces as an invoice nobody planned for. The 100% rule is the check that catches the missing box before it becomes the missing money.
How to think about it
At every box, ask two things: is there work in the parent that no child holds, and is there a child that is not really part of the parent. Then add the children's costs and compare them with the parent's.
Worked example
1.2 New building ready: $30,000The parent's figure.
1.2.1 $6,400 + 1.2.2 $9,600 + 1.2.3 $12,000 = $28,000The children add to $28,000.
$30,000 − $28,000 = $2,000 missingEither the parent is over-stated, or a child is missing. Look: nobody wrote signage installed. Add 1.2.4.
Your turn
Write the check the 100% rule asks at each box.
The children add to of the parent, no more and no less.
Solve one, graded on the server
The trap
Adding a miscellaneous child to make the numbers sum. It hides the missing package instead of finding it, and the invoice still arrives.