I’d also love to hear when this is added. Simply just a total on the bottom of the column would be so increadibly helpfull!
Note: Not a solution but marked as such to elevate a key reply
Hi @Thijs_Sturm , welcome to the forum 
With the Dashboard tab that was recently added to Portfolios you could create a chart based on your projects in the portfolios and select the count by your numeric custom field. This works best using ‘donut’ or ‘number’ type charts so the total will be visible.
Not as ideal as having a sum at the bottom of your Portfolio’s List view, but definitely more visually pleasing 
Hi everyone!
I’m thrilled to announce that the Portfolio list view will soon support column function, a feature that is currently available for Projects. This update will enable you to visually aggregate numeric custom field data in your portfolio, providing an at-a-glance overview of your work’s progress.
The column function will support the following options: Sum, Average, Minimum, Maximum, Count, or None (to disable the function).
Feel free to reach out via the Tips and Tricks category if you have any questions!
This update is being rolled out gradually and it will be available to all Business, Advanced, Enterprise and Enterprise+ customers soon!
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