Le Generateur de Formules Excel : Transformez un Calcul en Langage Simple en Formule Fonctionnelle
Pourquoi ce prompt est important
Hand-built spreadsheet formulas for board and finance decks fail quietly far more often than people expect. A SUM that drops a text-formatted cell, an AVERAGE that includes a header row, or a blank cell silently treated as zero can shift a reported KPI enough to trigger a strategic conversation based on a wrong number. Once a bad figure has been presented to finance or the board, correcting it afterward costs far more in credibility than the two minutes it takes to get the formula right and understand exactly why it works before you present it.
À quoi nous l'utilisons
You're a sales operations analyst at a mid-size SaaS company, working in a Google Sheets pipeline tracker with roughly 3,000 rows. Finance needs the weighted average discount percentage across all deals marked "Closed Won" in Q3, weighted by deal value, and a few rows have a blank discount field because a rep forgot to fill it in. The number is due in the quarterly business review deck in two hours, and you need a formula that handles the blanks correctly instead of silently including them as zero and skewing the average down.
Prompt
Act as a senior data analyst who has spent years cleaning up broken finance and sales spreadsheets and knows exactly how formulas silently fail. Context: I need a formula for the following calculation, described in plain English: [DESCRIBE THE CALCULATION YOU NEED, e.g. "weighted average discount percentage for all deals marked Closed Won, weighted by deal value"] Tool: [SPECIFY Excel (and version, e.g. Excel 365) OR Google Sheets] Relevant data: [DESCRIBE YOUR COLUMNS/RANGES OR PASTE A SAMPLE ROW, e.g. "Column G = deal stage, Column H = close date, Column I = discount %, Column J = deal value, data starts row 2, ends row 3000"] Edge cases to handle: [LIST ANYTHING THAT COULD BREAK A NAIVE FORMULA, e.g. "some rows in the discount column are blank," "some deal values are stored as text," "I only want deals closed within a specific date range"] Task: 1. Write the working formula, ready to copy and paste directly into the cell. 2. Break down what each part of the formula does, in plain English, step by step. 3. Flag anything in my data description that is likely to break this formula (mismatched data types, absolute vs. relative references, off-by-one range errors). 4. If the tool I specified has a simpler function available in a recent version that could replace an older-style formula, mention it as an alternative. 5. If there's a meaningful syntax difference between Excel and Google Sheets for this formula, note it even if I only asked about one. Constraints: Avoid volatile functions (OFFSET, INDIRECT, NOW, TODAY) unless the calculation specifically requires them. The formula must be copy-paste-ready with no placeholder text left inside it — resolve every range and condition using the data description I gave you. Assume I am an intermediate spreadsheet user: I understand basic functions like SUM and IF but don't regularly write nested array formulas. Output Format: - The Formula (in a code block, copy-paste ready) - Step-by-Step Breakdown (numbered, plain English) - What Could Break It (bulleted) - Excel vs. Google Sheets Note (only if relevant) - Simpler Alternative (only if one exists)
Résultat
The Formula (Google Sheets, weighted average discount for Closed Won deals in Q3, ignoring blank discount rows):
=SUMPRODUCT((G2:G3000="Closed Won")*(H2:H3000>=DATE(2026,7,1))*(H2:H3000<=DATE(2026,9,30))*(I2:I3000<>"")*I2:I3000*J2:J3000)/SUMPRODUCT((G2:G3000="Closed Won")*(H2:H3000>=DATE(2026,7,1))*(H2:H3000<=DATE(2026,9,30))*(I2:I3000<>"")*J2:J3000)Step-by-Step Breakdown
- The formula is built from two SUMPRODUCT calls: the top one calculates the sum of (discount × deal value) for qualifying rows, and the bottom one calculates the sum of deal value alone for the same rows. Dividing the first by the second gives a value-weighted average rather than a simple average.
- Each condition inside the parentheses — (G2:G3000="Closed Won"), the date range check, and (I2:I3000<>"") — evaluates to TRUE (1) or FALSE (0) for every row. Multiplying these conditions together means a row only contributes to the total if ALL conditions are true simultaneously.
- The (I2:I3000<>"") condition is what solves your blank-discount problem: any row where the discount cell is empty evaluates to FALSE, zeroing out that row's contribution entirely instead of treating a blank as a 0% discount, which would have dragged your average down incorrectly.
- The date range conditions (H2:H3000>=DATE(2026,7,1)) and (H2:H3000<=DATE(2026,9,30)) restrict the calculation to close dates within Q3 2026 specifically.
What Could Break It
- If the discount column (I) is formatted as text instead of a number (common when values are pasted from another system with a % sign as text), SUMPRODUCT will treat those cells as zero rather than throwing an error — check for left-aligned numbers in that column, which usually signals text formatting.
- If deal value (Column J) contains any blank or text cells within qualifying rows, the multiplication will silently zero out that row's contribution to both sums, which is usually fine but worth confirming isn't hiding missing data.
- The range G2:G3000 assumes your data never exceeds row 3000 — if new deals get added below that row, this formula will silently exclude them. Consider converting your range to a Table (Ctrl+T in Excel, or an equivalent structured range in Sheets) so the formula auto-expands.
Excel vs. Google Sheets Note: This exact formula works identically in Excel 365 and Google Sheets — SUMPRODUCT syntax is consistent across both. In older Excel versions (pre-2007), you may need to enter it as an array formula with Ctrl+Shift+Enter, but modern Excel and Sheets both evaluate it as a normal formula.
Simpler Alternative: If you only needed a straight sum-based condition without the weighting, SUMIFS would be simpler and faster to read — but because this calculation requires weighting by deal value, SUMPRODUCT is the correct tool here rather than a simplification.
La plupart des gens qui ont besoin d'une formule de tableur ne veulent pas vraiment apprendre la syntaxe des tableurs — ils veulent le bon chiffre dans la cellule, une explication a laquelle ils peuvent faire confiance, et la certitude qu'elle ne se cassera pas silencieusement la prochaine fois que quelqu'un ajoutera une ligne. Ce prompt est concu pour offrir exactement cela, et sa structure est deliberement pensee autour des endroits ou les demandes de formules echouent generalement.
Pourquoi ce prompt est structure ainsi
Le cadrage du Role — un analyste de donnees senior qui a passe des annees a reparer des tableurs financiers et commerciaux casses — compte parce qu'il oriente le modele vers une redaction de formule defensive plutot que vers la reponse techniquement correcte la plus courte. Un modele a qui l'on demande simplement ecris-moi une formule pour X renverra souvent quelque chose qui fonctionne sur des donnees propres et se casse des qu'une cellule vide ou un nombre au format texte apparait. Presenter le modele comme quelqu'un qui a personnellement debogue ces echecs l'amene a les signaler de maniere proactive plutot que d'attendre qu'on le lui demande.
La section Contexte separe explicitement la description du calcul, l'outil (Excel ou Sheets), la disposition des donnees et les cas limites en quatre entrees distinctes plutot qu'un seul paragraphe. C'est important car les demandes de formules echouent le plus souvent lorsque l'un de ces elements manque — quelqu'un decrit clairement le calcul mais oublie de mentionner un cas limite de cellule vide, et recoit une formule correcte en theorie mais fausse sur ses donnees reelles.
La liste des cinq taches se termine deliberement par une demande d'alternative plus simple et une note de syntaxe inter-outils. Les analystes ne savent souvent pas qu'une fonction qu'ils utilisent a ete remplacee par quelque chose de plus propre dans une version recente, ou que la formule qu'ils sont sur le point de coller dans Google Sheets utilise une syntaxe exclusive a Excel. Demander les deux a l'avance permet de detecter cela avant que cela ne devienne une erreur de copier-coller decouverte en pleine presentation.
Comment l'adapter
Pour un calcul beaucoup plus simple — une SOMME directe ou un NB.SI sans complexite de ponderation ou de gestion des cellules vides — le modele renverra correctement une fonction courte plutot que de fabriquer une complexite inutile avec SOMMEPROD ou des formules matricielles. La structure s'adapte aussi bien vers le bas que vers le haut.
Pour les calculs recurrents que votre equipe execute a chaque cycle de reporting, il vaut la peine de sauvegarder la formule finale ainsi que son explication etape par etape quelque part ou toute votre equipe peut s'y referer — cela transforme un prompt ponctuel en connaissance institutionnelle qui survit meme lorsque l'analyste original passe a un autre projet.