Labs · Power BI

Lab: Combine Three Monthly Bank-Statement CSVs from a Folder and Refresh When a Fourth Month Arrives

By Ravindra Bagale · Last updated: 8 October 2026

Suppose we are…

Suppose we are a young software engineer at Infosys in Pune who wants to track monthly spending. Our bank (for example HDFC or SBI) lets us download each month's statement as a CSV. We have January, February and March 2026. April's file will come next month, and we do not want to rebuild anything when it does.

The statements are sample data made up for practice: a salary credit, rent, a Swiggy order, the MSEDCL electricity bill, an Amazon purchase and a mutual fund SIP each month. No real account details are used.

Goal of this lab

By the end you will have:

• One table Bank with 18 rows from 3 files, plus a Source.Name column telling which file each row came from.
• A measure Total Debit by month: 28,089, 28,236 and 28,383.
• Added April by copying one file into the folder and clicking Refresh: 24 rows, Total Debit 113,238.

What you need (all free)

• Power BI Desktop on Windows.
• Download bank_statements_jan_mar.zip (Jan–Mar, 3 CSVs)
• Download bank_2026_04.csv (April, add later)
• 30 minutes.

The data: before and after

Before. Three separate files of 6 rows each in one folder.

After. One combined table. When April is dropped into the folder, one Refresh adds it.

The formula

When you click Combine & Transform, Power Query writes these main steps for you:

Source                  = Folder.Files("C:\PowerBI\BankStatements")
Filtered Hidden Files1  = Table.SelectRows(Source, each [Attributes]?[Hidden]? <> true)
Invoke Custom Function1 = Table.AddColumn(#"Filtered Hidden Files1", "Transform File", each #"Transform File"([Content]))
Expanded Table Column1  = Table.ExpandTableColumn(#"Removed Other Columns1", "Transform File", …)

In plain words:

1. Folder.Files makes a list of every file in the folder, one row per file.
2. Transform File is a small function built from the first file. It reads one CSV and promotes its headers.
3. The function runs on every file, and Expand stacks the results under each other.

So when April arrives, Folder.Files simply finds 4 files instead of 3. Nothing else changes.

And the one DAX line:

Total Debit = SUM ( Bank[Debit] )

Steps

1. Create the folder C:\PowerBI. Right-click bank_statements_jan_mar.zip → Extract All…, set the destination to C:\PowerBI and click Extract. Leave bank_2026_04.csv in Downloads for now.

   👁 What you should see: C:\PowerBI\BankStatements with three files: bank_2026_01.csv, bank_2026_02.csv, bank_2026_03.csv.

2. In Power BI Desktop: Home → Get data → More… → Folder → Connect. Browse to C:\PowerBI\BankStatements and click OK.

   👁 What you should see: a window listing the 3 files with columns such as Name, Extension and Date modified.

3. Click Combine & Transform Data. In the Combine Files window keep Sample File: First file and check Delimiter: Comma. Click OK.

   👁 What you should see: a query called BankStatements with columns Source.Name, Date, Description, Debit, Credit, Balance and 18 rows. On the left there is a new group, Transform File from BankStatements, with helper queries. Do not delete them.

4. Check the types. Date must have the calendar icon; Debit, Credit and Balance must show 123. If any is ABC, click the icon and choose Whole Number.

   👁 What you should see: empty Debit or Credit cells show null, for example the Credit of the Rent rows.

5. Rename the query to Bank (right-click → Rename) and click Home → Close & Apply.

6. Right-click Bank in the Data pane → New measure: Total Debit = SUM ( Bank[Debit] ).

7. Make a Table visual with Source.Name and Total Debit.

   👁 What you should see: bank_2026_01.csv 28,089, bank_2026_02.csv 28,236, bank_2026_03.csv 28,383, Total 84,708.

8. Save as Lab-09-bank-folder. Now April arrives: copy bank_2026_04.csv from Downloads into C:\PowerBI\BankStatements.

9. In Power BI, click Home → Refresh.

   👁 What you should see: a fourth row, bank_2026_04.csv 28,530, and Total 113,238. Table view shows Bank (24 rows). You added no step.

10. Add a Card with Total Debit and a Slicer with Description. Click Swiggy - UPI.

    👁 What you should see: the card shows 2,782 (640 + 677 + 714 + 751): Swiggy spending went up every month.

11. Save again.

Common mistakes

Self-check checklist

Try-at-home challenge

Source.Name is ugly in a chart. Make a proper Month column instead and show Total Debit by month in a column chart. Hint: in Power Query, select the Date column and use Add Column → Date → Month → Name of Month.

Samjla ka? Folder.Files lists the files, Transform File cleans one, Expand stacks them all, and Refresh picks up new months. Aata pudhe jaauya: turn a hard-coded file path into a parameter.