CSV, IIF and the formats accounting data travels in

When accounting data leaves one system for another, it travels as a file — and the file’s format shapes what can go in it and how cleanly it lands. You don’t need to be a programmer to work with these, but knowing what each one is saves a lot of confusion.

CSV — the universal plain text

CSV (comma-separated values) is the lingua franca of data exchange: a plain-text table where commas separate columns and each line is a row. Almost everything can read and write it, which is why QuickBooks Online and countless tools import lists via CSV. Its simplicity is also its limit — a CSV is just a grid; it carries no built-in understanding of accounting relationships, so field mapping during import matters.

IIF — QuickBooks Desktop’s native format

IIF (Intuit Interchange Format) is a tab-delimited text format built specifically for QuickBooks Desktop. It can carry lists and certain transactions, which makes it powerful — but it’s strict and unforgiving: exact headers, references that must already exist, and little validation before it writes. A detailed comparison lives in IIF vs CSV.

Excel and others

Excel files (XLSX) are common as a working format — readable, easy to clean — but usually converted to CSV for import. Some systems export their own formats or via database queries, but they generally funnel down to CSV or a system-specific format for the actual load.

Why the format is the easy part

Here’s the thing people get backwards: the format rarely causes the real trouble. Clean, correctly structured data imports through either CSV or IIF; messy data fails through both. The hard part isn’t choosing a format — it’s preparing data that’s complete, correctly typed and de-duplicated, so whatever format you use, it lands right.