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How to use LAMBDA with REDUCE for cumulative math in Excel and Google Sheets
Topic:LAMBDA (reusable formulas)Excel & Google Sheets
=REDUCE(0, A2:A6, LAMBDA(acc, x, acc + x * 1.1))Try it with your data
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Step by step
- 1Enter the values you want to accumulate in A2:A6 (e.g. 100, 200, 150, 300, 250).
- 2Choose a starting value (the initial accumulator). Use 0 for sums, 1 for products.
- 3In B2, enter =REDUCE(0, A2:A6, LAMBDA(acc, x, acc + x * 1.1)) to sum values each inflated by 10%.
- 4The LAMBDA receives two arguments: acc (the running total so far) and x (the current element). The body defines how to combine them.
- 5REDUCE returns ONE value — the final accumulator — not an array. Use SCAN instead if you need every intermediate step.
Tips
- REDUCE is powerful but slower than native aggregates like SUM or PRODUCT for simple math — use those when no custom logic is needed.
- The initial accumulator (first argument) matters: for multiplication start with 1, for string concatenation start with "" (empty string).
- Nesting REDUCE inside another function is valid — e.g., wrap it in TEXT() to format the result directly.
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Frequently asked
How is REDUCE different from SCAN?
REDUCE returns only the final accumulated result. SCAN returns the accumulator value at every step, giving you the full running history as an array.
Can I use REDUCE to concatenate text?
Yes. Set the initial value to "" and the LAMBDA body to acc & ", " & x. This is slower than TEXTJOIN for simple cases, but REDUCE allows conditional logic (e.g. skip blank cells).
Does REDUCE support 2-D arrays?
REDUCE flattens 2-D ranges row by row, so it processes all cells sequentially. Use BYROW first if you need per-row reductions before a final fold.
More on LAMBDA (reusable formulas)
See all →Reference
LAMBDA
Defines a reusable custom function using named parameters and a formula body, letting you call it like any built-in function — no VBA or scripts needed.
How-toHow to write a recursive LAMBDA function
Build self-referencing recursive functions using LAMBDA with the Excel Name Manager or Google Sheets named functions — for tasks like factorial, Fibonacci, or tree traversal.
How-toHow to use LAMBDA with MAP across a range
Use MAP with a LAMBDA to apply a custom formula to every cell in a range in Excel 365 and Google Sheets, returning a transformed array without helper columns.
How-toHow to use LAMBDA with SCAN for a running balance
Use SCAN with a LAMBDA to compute a running balance or cumulative total in Excel 365 and Google Sheets, returning one result per row without helper columns.
How-toHow to use BYROW and BYCOL to apply a LAMBDA per row or column
BYROW and BYCOL apply a LAMBDA to each row or column of a range in Excel 365 and Google Sheets, returning a per-row or per-column result without helper rows or columns.
How-toHow to use MAKEARRAY with LAMBDA
MAKEARRAY generates a 2-D array of any size in Excel 365 and Google Sheets by calling a LAMBDA with each row and column index, letting you build multiplication tables, calendars, or computed grids.