What QFX is
OFX is the format behind the Download Transactions button on your bank's website. Version 1 is SGML, where a leaf element has an opening tag and no closing one. Version 2 is real XML. QFX is Intuit's variant of the same thing with a few extra tags, which is why a .qfx file opens in Quicken and is refused by software that only knows plain OFX.
Retail banks, credit card issuers and brokerages, because it is what Quicken and Microsoft Money asked for and the industry standardised on.
What Excel is
An Excel workbook is a zip archive of XML parts describing sheets, cells, formulas, styles and charts. The .xlsx extension is that format; .xls is the older binary one from before 2007.
Finance, operations and anyone who received a file from finance or operations.
What changes when you convert QFX to Excel
Each STMTTRN block becomes a row: date, amount, type, payee, memo, cheque number and the bank's own transaction id. The account number and currency come from the statement header and are added to every row, so a file merged with another still says which account it came from. Both the SGML and the XML flavour are read the same way.
You get a single sheet with a header row and column widths sized to the content. Values are written as text unless type inference is on, which keeps identifiers like 0044 or 007 intact.
Each transaction becomes a row with its date, amount, type, payee, memo, cheque number and the bank's own transaction id. That id is worth keeping: it is the only field guaranteed unique, which makes it the right key when you reconcile two downloads that overlap.
Dates arrive as YYYYMMDD with a time and timezone after them, which is unambiguous, so they are reformatted to YYYY-MM-DD. That sorts correctly as text and means Excel will not reinterpret them according to whichever locale the machine is set to.
Amounts keep their sign as the bank wrote it. A debit is negative. Nothing is rounded, reformatted or converted, and the currency from the statement header is added as its own column.
What carries over from QFX to Excel
One property of the OFX has no home in Excel, and it is worth knowing which before you convert.
OFX can hold a value that is itself a list or an object. Excel has only flat cells, so nested values are flattened into one cell rather than being spread across columns.
Both formats record types, so numbers, booleans and nulls survive as themselves rather than as text.
Why your bank charges for this file
QFX is OFX with a few Intuit-specific tags added, the important one being a bank identifier that Quicken checks before it will accept the file. The transactions inside are identical to the free OFX or CSV download. Many banks charge a monthly fee for the QFX version anyway.
If your bank offers OFX, QIF or CSV as well, any of them converts here and none of them costs anything.