Get every statement into the same column layout
Before you can combine anything, each statement needs the same columns in the same order. A workable layout is: Date, Description, Amount, and optionally Balance and Account. If one file uses separate Debit and Credit columns while another uses a single signed Amount column, decide on one convention and convert the others to match.
If your statements are PDFs, convert each one to CSV or Excel first. Bank PDFs vary a lot in structure, so check that dates land in the date column and that amounts are read as numbers, not text. A common problem is a thousands separator or currency symbol turning an amount into text, which then will not add up.
Add an Account column to every file and fill it with the account name or last four digits before you merge. Once rows from three accounts sit in one sheet, you will not be able to tell them apart without it. This one extra column saves hours later.
Standardize dates and amounts
Dates are the most common thing that breaks when merging. One statement might use MM/DD/YYYY and another DD/MM/YYYY, and a spreadsheet cannot tell them apart on its own. Confirm the format of each file, then convert everything to a single real date format your spreadsheet recognizes. Sorting by date only works once all dates are true date values, not text.
For amounts, pick a single signed convention: money out is negative, money in is positive. If a file has separate Debit and Credit columns, create one Amount column and use a formula so credits stay positive and debits become negative. Strip out currency symbols and stray spaces so every value is a clean number.
Do a quick sanity check on each file before combining. Total the Amount column for one statement and compare it to the change in balance shown on the paper statement. If they match, that file is clean and ready.
Combine the files into one sheet
The simplest method is to open your target spreadsheet, keep one header row at the top, and paste each statement's rows underneath the last. Because every file now shares the same columns, the rows stack cleanly. Repeat for each statement until all transactions sit in one continuous list.
If you have many files or expect to repeat this monthly, a tool like Power Query in Excel can append multiple files automatically. Point it at a folder, map the columns once, and it stacks new files as you drop them in. Google Sheets users can achieve similar results by importing each CSV to a tab and stacking them with a formula.
After combining, sort the whole table by date, then by account. Scan for obvious gaps or duplicate rows, which happen when statement periods overlap. Delete any transaction that appears twice from an overlapping date range.
Verify the merged total and finish up
The final check is arithmetic. Sum the Amount column across the entire merged sheet and compare it to the sum of the individual statement totals you calculated earlier. If they match, no rows were lost or duplicated during the merge.
Turn the range into a table or add filters so you can slice by account, date range, or description. A pivot table gives you monthly totals per account in a few clicks, which is useful for cash-flow summaries and category reviews.
Save a clean master copy and keep your original statement files untouched. If you later import into QuickBooks, Xero, or Wave, most accounting tools accept a CSV with Date, Description, and Amount columns, so a well-built merged sheet doubles as an import source.