Best way to get rolling 12-month totals

At the simplest level, this has worked for me for years. 

=SUM(C207:C218)

I'm at row 218 right now in a spreadsheet containing a multi-year monthly summary of increases/decreases in my IRA. There's a column for changes in market value, a column for dividends and interest, for withdrawals. Then, off to the side, I calculate the rolling 12 month totals in each of those categories.

So, to spell this out one step further, C207 contains the monthly market increase for October, 2024; C218 contains September 2025 data. The intervening rows contain the other ten months.

Since each row is a single monthly total, copying the formula down changes the relative references so they always are the rolling 12 months including the last or current. 

As noted, this is the ultimate in simplicity and assumes that each row we're working with already contains one month, and that monthly rows are contiguous with no blanks or other extraneous rows.