Most often this happens due to three mistakes: the data source hasn't expanded to include new rows, there are empty rows in the source, or a forgotten filter is active in the pivot table.

Check whether the source range is formatted as a "smart table" (Ctrl+T). If not, the pivot table will use a static address and ignore new entries.

The second most common reason is a completely empty row or column that breaks the continuous data array. If the source is fine, click on the funnel icons in the pivot table fields — the data might be hidden by a filter.

A more in-depth breakdown of all the basics is available in the complete guide to pivot tables for beginners.

🔗 Source: excel.rf