Solved: How to use Notion Formulas 2.0 to calculate a weighted project completion percentage from a related tasks database

📌 The Problem Explained

In standard project management, many users rely on a simple percentage (Completed Tasks / Total Tasks). However, this method assumes all tasks are equal. In reality, a “Fix Typo” task might take 5 minutes, while a “Build Homepage” task takes 20 hours.

Without weighted formulas, your project progress bar will show 50% completion even if the two remaining tasks are the most labor-intensive parts of the project. To get an accurate picture, you need to assign a Weight (effort, points, or hours) to each task and calculate progress based on the sum of weights of completed tasks versus the total potential weight.

💡 The Quick Solution

Assuming your Projects database is related to a Tasks database, and your tasks have a Weight (Number property) and a Status (Checkbox or Status property), use this formula in your Projects database:

let(
  totalWeight, prop("Tasks").map(current.prop("Weight")).sum(),
  doneWeight, prop("Tasks").filter(current.prop("Status") == "Done").map(current.prop("Weight")).sum(),
  if(totalWeight > 0, doneWeight / totalWeight, 0)
)

Note: Change "Status" == "Done" to match your specific status name or use current.prop("Done") == true for checkboxes.

🛠️ Step-by-Step Breakdown

1. Database Preparation

Ensure your databases are structured as follows:

Database	Property Name	Property Type
Tasks	Status	Status (or Checkbox)
Tasks	Weight	Number (representing effort)
Projects	Tasks	Relation (to Tasks database)
Projects	Progress	Formula

2. Implementation Steps

Step	Action	UI Path
1	Open your Projects database and add a new property.	+ Add a property > Formula
2	Name the property “Weighted Progress” and click Edit.	Property Name > Edit Formula
3	Paste the code from the “Quick Solution” above into the editor.	Formula Editor
4	Set the number format to percentage.	Edit Property > Number format > Percent
5	Enable the progress bar or ring visualization.	Edit Property > Show as > Bar

3. Understanding the Formula Logic

• let(...): This creates variables (totalWeight and doneWeight) to keep the formula clean and readable.
• .map(current.prop("Weight")): This looks at every related task and “grabs” the number in the weight column.
• .filter(...): This isolates only the tasks that meet your “Completed” criteria.
• .sum(): This adds the extracted weights together.
• if(totalWeight > 0...): This prevents a “Divide by zero” error if a project has no tasks assigned yet.

⚠️ Common Mistakes to Avoid

• Empty Weight Values: If you leave the Weight property empty on a task, Notion treats it as 0. This will skew your percentage. Ensure every task has at least a weight of “1” for a baseline.
• Mismatching Status Names: If your Status property uses “Complete” instead of “Done,” the .filter() function will return 0. Double-check that the text inside the quotation marks matches your status label exactly.
• Circular Relations: Ensure you are pulling the weight from the Tasks relation and not trying to reference a Rollup. Formulas 2.0 can access related data directly, making Rollups unnecessary for this calculation.