Array Formula Performance Review
Speed up slow workbooks.
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Review my workbook for slow formulas. App and version: [SPREADSHEET_APP_AND_VERSION]. Symptoms (recalculation time, freezing): [SYMPTOMS]. Workbook size and structure (rows, sheets, number of formulas): [WORKBOOK_SIZE]. The slowest formulas or types I suspect: [SUSPECT_FORMULAS]. Diagnose using this order: 1. Volatile functions (INDIRECT, OFFSET, TODAY, NOW, RAND) spread across many cells; replace with stable references or a single cell for TODAY. 2. Whole-column references in lookups and SUMIFS on large data; limit to the used range or use tables. 3. Repeated heavy calculations: compute once in a helper column and refer to it, or use LET. 4. Lookups on unsorted large data repeated per row; use a keyed approach, XLOOKUP with binary search on sorted data where valid, or move to a pivot or a query. 5. Array formulas covering thousands of rows with nested lookups; reduce the range or use helper columns. 6. Excess conditional formatting rules and data validation across entire columns. 7. Many cross-workbook links and imports. 8. Calculation mode: manual during editing, automatic otherwise; iterative calculation off unless needed. Return a table: Issue | Evidence | Fix | Expected benefit | Risk. Add a before-and-after timing plan (measure recalculation time), a safe approach (work on a copy, keep results identical, compare outputs), and when to move to a database or script. Do not alter formulas without a copy.
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