I would like to add a calculation function to a custom module for my users to record their sales by week, there is a total sales column of MTD forecast sales and MTD actual sales to sum up all the weekly forecast and actual sales the user has recorded, anyone can help?
You can’t create a calculated field like your thinking. However, you can create a workflow that adds up the fields and updates the “total” field equal to the sum of the entered forecasts on save.
Here’s a link to the guide. I’ve done this for one of my clients before. It takes a bit of trial and error but it works pretty good.