// Sheets

Auto-fill the date when a row is edited in Google Sheets.

Stamp today's date into column B the instant column A gets a value — without writing into already-stamped rows. Pure onEdit trigger; nothing leaves the sheet.

“When I add a new entry I want the timestamp to fill itself. I'm tired of typing =NOW() and pasting as value.”

The script

copy · paste · trigger

autoFillDateOnEdit.gs

Apps Script

// Installable onEdit trigger. When a value lands in column A,
// stamp today's date into column B (only if B is empty so existing
// timestamps aren't overwritten on re-edit).
function onEdit(e) {
  const range = e.range;
  if (range.getColumn() !== 1) return;  // only column A
  if (range.getRow() === 1) return;     // skip header row
  if (!range.getValue()) return;        // ignore deletions

  const dateCell = range.offset(0, 1);  // adjacent column B
  if (!dateCell.getValue()) {
    dateCell.setValue(new Date());
  }
}

Generate yours

Need a variant? Gnaw writes a custom version from one sentence — fields, triggers, edge cases handled.

Walkthrough

How it works

Apps Script ships two onEdit variants. The simple trigger (just a function named onEdit) fires on every edit but can't write to other documents. The installable trigger has the same name but is added explicitly via the Triggers panel — it can do almost anything.

For this script the simple trigger is enough: we only write within the same sheet. Apps Script auto-detects the function name and wires it up.

The three guards (column check, header check, deletion check) keep the trigger from firing on irrelevant edits. The B-cell-empty check makes the function idempotent — editing column A in an existing row won't overwrite a date that's already there.

How to install

Paste the function into Extensions → Apps Script for the sheet. Save. That's it — the simple onEdit trigger fires automatically on the next edit. No "Add Trigger" step needed.

If you ever need to write into a different sheet (e.g. mirror the timestamp into a log workbook), switch to an installable onEdit trigger via the Triggers panel — same function body works.

Tweaking the columns

Watch a different column: change the `getColumn() !== 1` check.

Stamp into a different column: change `range.offset(0, 1)` (the second argument is the column delta — 1 = right by one, 2 = right by two, -1 = left by one).

Stamp the time without the date: replace `new Date()` with `new Date().toLocaleTimeString()`.

Want a custom version?

Describe your sheet and the rule you want. Gnaw writes the Apps Script — fields, triggers, edge cases — in one shot.

Generate yours Browse BullPack

FAQ

4 questions

Why doesn't the date update when I change column A again?: By design — the script checks if column B already has a value and skips if so. Remove the `if (!dateCell.getValue())` block to make every edit re-stamp.
Can I do this with a formula instead?: =NOW() in column B works, but it volatilises — every recalculation moves every timestamp. Apps Script writes a static value that survives recalc.
Will this work in shared sheets with multiple editors?: Yes. Each editor's edit fires the trigger under their own credentials. The stamps reflect "when the row was first edited," not who.
How do I capture the editor's email too?: Switch to an installable onEdit trigger and use Session.getActiveUser().getEmail() inside the handler. The simple trigger can't read user identity.