How to use the Convert Excel Date Numbers to Dates
Join files on a key, trim, concatenate, fix dates, filter and more, in the order you choose.
Data Transformation lets you reshape a file with a list of steps instead of formulas. Join two files on a key with an inner, left, right or full join, trim spaces, concatenate or split columns, change date formats, change case, find and replace, filter, sort, remove duplicates and fill empty cells. See the result straight away, then download it or send it to another tool. Every step is recorded in Data Lineage.
Load a file (and a second one to join)
Add the transformations you want
Check the result and download
Tips
Joins match keys ignoring case and spaces.
Add Trim spaces before a join if keys have stray spaces.
Excel stores dates as the number of days since 1900. When a file is saved as CSV, those numbers can show up instead of dates. The date step turns them back into dates.
Does it handle unix timestamps?
Yes. Ten-digit values are read as seconds and thirteen-digit values as milliseconds.
Can I join two files or combine columns?
Yes. Data Transformation lets you join two CSV or Excel files on a key (inner, left, right or full), and trim spaces, concatenate columns, change case, find and replace, split, rename, filter, sort, remove duplicates and fill empty cells. You choose the steps, check the result and download it. Your files stay in your browser.
Which transformations are available?
Join with a second file (inner, left, right or full), trim spaces, concatenate columns, change date formats, change text case, find and replace, split a column, rename or remove columns, filter rows, remove duplicates, sort and fill empty cells. Steps run from top to bottom and you can reorder them.
Can I change the date format of a column?
Yes. Add a Change date format step, pick the column and the new format, such as 2026-03-09, 09/03/2026 or March 9, 2026. It reads many layouts, Excel date numbers and unix timestamps, and can also give only the year, month, weekday or quarter. If 03/04/2026 is unclear, you choose day first or month first.
Is Data Transformation a VLOOKUP alternative?
For lookups between two files, yes. A join adds the matching columns from the second file to every row of the first, with no formulas. Keys are matched ignoring case and extra spaces.
Related pages
Data Transformation: Join, Trim, Concatenate: Join two CSV or Excel files on a key, trim spaces, concatenate columns, filter, sort and more. Pick your steps and download the result. Free, in your browser.
Change Date Format in a CSV File: Change the date format of a column in a CSV or Excel file, for example 09/03/2026 to 2026-03-09, or get only the year or month. Free, in your browser.
Join Two CSV Files on a Key: Join two CSV or Excel files on a key column with an inner, left, right or full join. Free, and your files stay in your browser.
Merge CSV Files by a Common Column: Merge two CSV files into one by matching a common column such as id or email. Choose inner, left, right or full. Free, in your browser.
VLOOKUP Alternative for CSV and Excel Files: Look up values from one file in another without VLOOKUP. Join two CSV or Excel files on a key and add the columns you need. Free, in your browser.
Join Two Excel Files on a Key Column: Join two Excel files on a key column and download the combined result as Excel or CSV. No formulas, free, and your files stay in your browser.
Concatenate Columns in a CSV File: Combine two or more CSV columns into one with the separator you choose, such as first and last name. Free, in your browser, nothing uploaded.
Trim Spaces in a CSV File: Remove extra spaces from every cell or only the columns you pick in a CSV or Excel file. Free, in your browser, and the file is never uploaded.