Hi jandrewn,
Based on your description, after filtering data from you table and you use the formula to sum the data, but the total result is wrong.
I suppose you wonder to sum the visible data in your table.
I suggest use the SUBTOTAL formula instead of SUM formula to get the total result as shown in the following figure.
=SUBTOTAL (109,f1:f1426)
If my understanding is incorrect, please upload a sample via OneDrive or a screenshot so that I can get more accurate solutions to this problem.
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ibsofc@microsoft.com I'd like to help you check it.
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Im glad to help you and follow up your reply.
Regards,
George Zhao
TechNet Community Support