XLS to XLSX moves values, not the whole workbook
Excel 2007 and later, Google Sheets, and most imports want XLSX. An old .xls file is the blocker.
The workbook is read in the browser and written as XLSX. Values move. Charts and some old macros do not.
Dates and extra sheets after XLS to XLSX
Check dates and leading zeros after you open it. A password-protected workbook will not open here.
A related step, if you still need one, is XLSX to XLS.
When XLS to XLSX is the right page
XLS to XLSX sits on this site because XLS and XLSX are not interchangeable, even when they look similar in a file list. Excel 2007 and later, Google Sheets, and most imports want XLSX. An old .xls file is the blocker. You only need XLS when a named program refuses XLSX. Spreadsheets, charts, and CSV exports start here for most offices in 2026.
The workbook is read in the browser and written as XLSX. Values move. Charts and some old macros do not.
What you give up by leaving XLS
XLS is the Excel format from before 2007. Some accounting tools still require the old extension. Very large sheets can hit the old row limit and drop data. Macros and modern charts do not survive.
Prefer XLSX whenever the other side allows it.
What you gain, and do not gain, with XLSX
The download has to be XLSX, because that is the format the next step named. Spreadsheets, charts, and CSV exports start here for most offices in 2026. Values, dates, and several sheets can travel when the tool writes a real workbook.
Afterward, check dates, leading zeros, and whether a second sheet was left behind.
A test that matches the real file
Start from the question the other software asked. If it asked for XLSX, XLS to XLSX is the matching page. If it asked for something else, switch tools instead of hoping a similar extension will pass. Excel 2007 and later, Google Sheets, and most imports want XLSX. An old .xls file is the blocker. The workbook is read in the browser and written as XLSX. Values move. Charts and some old macros do not. The limit is the part people skip, and it is the part that decides whether the download is usable. Check dates and leading zeros after you open it. A password-protected workbook will not open here. The file stays in your browser and is not uploaded. The limit is 100 MB. Keep the original until the download has been opened in the program that will use it. Check three things in the download: it opens, the XLS material you cared about is still there, and the file size or the layout is what the form described. A new extension alone is not those three things. If a portal, a teacher, or a client rejects the file, send them the original XLS as well when you are allowed to. XLS to XLSX is a convenience copy. It is not a new master. Spreadsheets break at quiet places: a second sheet, a date that changed, a leading zero that vanished, a comma inside a name. After XLS to XLSX, open the result in a text editor as well as Excel. Excel guesses types and hides the delimiter. The workbook you calculated in is still the master.
Here is the decision for XLS to XLSX. You start with XLS and you stop when a real program accepts XLSX. A simple sheet of values can move into the old format. A conversion aimed at CSV or JSON flattens that richness. Charts and macros are not the point. If those two sentences describe a tradeoff you do not want, do not convert. Renaming the extension by hand will not do this job. Running the tool twice on its own output will not do it either.
Check dates and leading zeros after you open it. A password-protected workbook will not open here.
A related step, if you still need one, is XLSX to XLS.
Other jobs start from the homepage, where each tool is named for the conversion it actually does.