= Write My Formula

Data validation formula generator

Write the custom formula for a data validation rule.

Describe the entries that should be allowed, paste the columns involved, and get a TRUE/FALSE formula for Excel or Google Sheets data validation.

Request

Formula request

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Mode
Spreadsheet
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Purpose-built inputs

A focused workflow for everyday spreadsheet work.

Structured formula builder

Task, table context, target range, and function hint keep the request specific.

Write / Explain / Fix modes

Generate a new formula, translate a pasted one, or diagnose common syntax issues.

Excel and Sheets toggle

Compatibility notes call out modern functions and platform-specific behavior.

Formula-bar output

The result is formatted for scanning and placed next to a copy button.

Common formulas

Pick the formula you came for.

Percentage formulas

Build percent of total, percent change, discount, markup, tax, tip, and completion-rate formulas.

Date formulas

Create due dates, workday counts, month-end dates, date differences, and overdue checks.

FILTER formulas

Return matching rows for status, region, date, text, and threshold conditions.

Text formulas

Split, extract, join, trim, clean, and replace text from messy imported cells.

Data validation formulas

Block bad IDs, duplicate values, missing fields, and invalid entries with custom TRUE/FALSE rules.

XLOOKUP formulas

Return matching values with separate lookup and return ranges.

INDEX MATCH formulas

Build flexible lookup formulas for left lookups, two-way lookups, and older Excel files.

SUMIFS formulas

Total rows that match status, date, category, customer, or region rules.

Use case

Data validation formula generator for spreadsheet work.

Build custom data validation formulas that return TRUE for entries users are allowed to type and FALSE for entries that should be rejected.

What this page gives you

  • A draft custom validation formula matched to the entry rule you describe.
  • A plain-English read of why the rule returns TRUE for accepted values.
  • Checks for blanks, duplicate handling, pattern tests, and first-cell references.

When to use it

Use this page when spreadsheet users should be stopped from entering invalid values, such as duplicate IDs, malformed emails, dates outside a window, or required fields left blank. Include the first cell of the validation range because custom formulas are evaluated relative to that starting cell.

Do not use a validation formula when you only need to highlight existing bad data. Conditional formatting is better for visual review, while data validation is better for blocking future entries.

Worked example

For customer IDs entered in C2:C500, a data validation rule can require the ID- prefix and a minimum length.

=AND(LEFT(C2,3)="ID-",LEN(C2)>9)

The formula returns TRUE only when the entry in C2 starts with ID- and has more than 9 characters, so the same relative rule can be applied down the validation range.

Check before you paste

  • Data validation custom formulas should return TRUE for allowed entries.
  • Write the formula as if it is evaluated from the first cell in the applied range.
  • Check whether your rule should reject blanks or let users leave the cell empty.

Upgrade when the work piles up

Keep going when the sheet gets complicated.

Try twice as a guest. Free accounts get 3 runs per week plus a monthly product email. Upgrade when formula work becomes a recurring part of the week.

Founding access

$9

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