When you need one date to represent a month, calculate its first day. This gives you a consistent key for grouping records and comparing monthly periods.
The calculated field
Create a calculated field named Month start:
DATE(DATETRUNC('month', [Order Date]))DATETRUNC reduces the value to the beginning of the month. Wrapping it in DATE returns a date value.
| Order Date | Month start |
|---|---|
| 2026-09-15 | 2026-09-01 |
| 2026-09-30 | 2026-09-01 |
| 2026-10-01 | 2026-10-01 |
Use a date field
Replace [Order Date] with your own date or datetime field. The other date guides in this series use [US Release Date] from the Star Wars saga workbook.
Calculation versus formatting
This changes the date value. If you only need to display a date as a month name, adjust its formatting instead. Keeping a complete month-start date also preserves the year, so September 2025 and September 2026 remain separate.
