How can I automate adding subtotals in the next column

I am trying to add subtotals in the next column. The data is a little large spanning across 10k rows. How can I automate?

as i think you don’t ask for C100: ‘=SUM(B10;B20;B30;B100)’ it would be helpful to give a more detailed description of your case …

To add a subtotal at each row: If data are in A2:A10000, type in B2 =A2, and in B3 =B2+A3, then copy B3 until B10000.

See sample file: subtotal in next column.ods. Colored cells have formulas.

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