Format Timestamps in Excel Files Online

What timestamp formats does the Excel timestamp tool support?

ISO 8601, Unix epoch (seconds and milliseconds), US date (MM/DD/YYYY), European date (DD/MM/YYYY), and any custom format using strftime patterns.

What if the tool does not recognise the date format in my Excel file?

Enter a custom strftime pattern in the format field. For example %d/%m/%Y %H:%M:%S matches 31/12/2024 23:59:59. The strftime reference covers all supported tokens.

Does the Excel timestamp tool convert time zones?

No. The tool reformats how a timestamp is displayed but does not shift values between time zones. For timezone conversion use the SQL Query tool with AT TIME ZONE.

Is my data private?

Yes — completely. Your file is never uploaded to any server. Everything runs locally in your browser using WebAssembly — processing happens entirely inside your tab. Once you close the tab, nothing is retained.

What is the maximum file size?

The free limit is 50 MB. For larger files, performance depends on your device's available memory — most modern machines handle 500 MB to 1 GB comfortably.