How to split a CSV by month in Excel

These steps assume a CSV with a Date column in column A containing real Excel dates, such as the CSV from the converter. If your dates are text, fix them first: see opening a CSV without breaking dates.

Step by step

1. Make it a tableClick any cell in the data and press Ctrl+T (Cmd+T on a Mac). Tick “My table has headers”. Tables extend formulas automatically.
2. Add a Month columnIn the first empty column, type the heading Month, and in the row below enter =TEXT([@Date],"yyyy-mm"). Every row gets a month such as 2026-03, which sorts correctly.
3. Filter to one monthUse the filter arrow on the Month column to show a single month. Select the visible rows and copy them to a new sheet if you need a separate file.
4. Or summarise every month at onceInsert a PivotTable, put Month in Rows and Paid in and Paid out in Values (set to Sum). You get a month-by-month summary in one go.
5. Or make one sheet per month automaticallyIn Excel 365, on a new sheet, use =FILTER(Table1, Table1[Month]="2026-03"). The sheet updates if the table changes.
6. Save separate CSV files if neededFor software that needs one file per month (or has an upload size limit), copy each month to a new workbook and use File, Save As, CSV UTF-8.

Tax years and quarters

For a UK tax year, filter dates from 06/04 to 05/04 rather than by month. For VAT quarters, add a Quarter column with ="Q"&ROUNDUP(MONTH([@Date])/3,0), or a column based on your own VAT period dates.

Google Sheets

The same approach works: =TEXT(A2,"yyyy-mm") for the month, Data, Create a filter, and Insert, Pivot table. FILTER works too.