Auto-adjust # of rows in a column that have a formula based on adjacent column data?

So I have a table of transactions with category, description, data, amount, etc.

I am using UNIQUE() on another sheet to generate only the unique va balues from that list of transactions as categories repeat many times (many lines for Groceries, many for gas, for gym, etc etc). I am actually using UNIQUE(IFERROR(FILTER())) to filter out lines from the first table that omicanly fall between certain reference dates (IE give me all unique categories from 5/1/18 to 5/31/18).

Once I have my unique list on another sheet, I am using a SUMIFS() to sum all transactions against each unique category (this is a budgeting sheet).

What I am struggling with is every month, the list of unique values is a different length. Basically I am creating a live dynamic pivot table (I will do some other calcs off this data afterwards), but because one month might have 7 unique categories but the next month could have 13 or 12 or 20, I need the adjacent column which has the SUMIFS() formula to scale up and down based on the unique category column. Is there a way to tie those two together dynamically so if the UNIQUE() function returns 15 lines (A5-A20 for example), then the SUMIFS() will fill B5-B20? Obviously I can just populate a "fill down" in the B column for like 100 rows, but I want it to be dynamic so I can have a total line at the bottom. Again, this is basically recreating a pivot table but for some formatting and later calc reasons I have not gotten a pivot table to work as I would like. Can this be done without scripting?

Any thoughts?

Thanks for the response mate. Actually looking to do this on google sheets. Was thinking the arrayformula() deal would cause the autofill down like when adding data via a form, but so far no dice.

Maybe I need to be looking specifically into how to manipulate pivot tables more, but I've always had trouble running formulas against the pivot table (IE doing a fill down keeps the reference to the original pivot table cell instead of transferring the reference down, and everytime I refresh data the format reset). Also I do prefer the pivot table format in excel over google sheets but this doc has to live in sheets (personal budget).