How to sum every nth row
✓ Verified in LibreOffice 25.8.7.3 ✓ Verified in Google Sheets (2026-08-30)Add up every 2nd, 3rd, or nth value in a column — common with repeating blocks of data.
The formula
| App | Formula | Notes |
|---|---|---|
| Excel (desktop) | =SUMPRODUCT((MOD(ROW(B2:B7)-ROW(B2),3)=0)*B2:B7) | Change the 3 to your n. Anchoring on ROW(B2) makes the first row count as position 0. |
| Google Sheets | =SUMPRODUCT((MOD(ROW(B2:B7)-ROW(B2),3)=0)*B2:B7) | Identical. |
| LibreOffice Calc | =SUMPRODUCT((MOD(ROW(B2:B7)-ROW(B2),3)=0)*B2:B7) | Identical. |
How it works
ROW(B2:B7)-ROW(B2) numbers the rows 0,1,2,3,4,5 regardless of where the range starts; MOD(...,3)=0 is true for positions 0 and 3 — every 3rd row. SUMPRODUCT multiplies those TRUE/FALSE values (1/0) by the numbers and sums: 10 + 40 = 50. Every-other-row is the same formula with 2, and MOD(...,3)=1 shifts the starting offset.
Verified, not just documented
We ran =SUMPRODUCT((MOD(ROW(B2:B7)-ROW(B2),3)=0)*B2:B7) in LibreOffice 25.8.7.3 (headless, with forced recalculation) and it returned 50 — exactly the expected result. We then ran the same formulas in Google Sheets, executed 2026-08-30: a formula-only workbook goes into Google Drive, which converts it to a Sheet and recalculates every formula with Google’s own engine, and comes back out as .xlsx carrying the values Google computed. It returned 50 for the worked example, the same value LibreOffice produced. Both engines’ numbers on this page are executed results. The Excel formula follows Microsoft’s official documented syntax — we do not run desktop Excel.
Functions used
SUMPRODUCT · MOD · ROW — see full Excel, Google Sheets & LibreOffice compatibility for each.
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