Does this support Excel's 1900 leap-year bug?

Yes. The Windows 1900 mode accounts for Excel serial 60 and the leap-year compatibility behavior.

Can it convert fractional serial dates?

Yes. Fractional serial values are converted into time of day.

Excel Serial Date Converter

Convert Excel date numbers to readable local dates, or convert a local date and time back to an Excel serial value. Supports Windows 1900 and Mac 1904 systems.

Runs entirely in your browser. No spreadsheet upload, no account, no server processing.

Excel serial number

Local date and time

Date system

Local Date

UTC ISO

Excel Serial

Date System

Excel serial date details

Excel stores dates as serial numbers. Whole numbers represent days and fractional values represent time of day. Windows spreadsheets usually use the 1900 system; older Mac spreadsheets may use 1904.

FAQ

What is serial 60? In Windows 1900 mode, Excel preserves a historical leap-year compatibility issue. This converter accounts for that behavior.

Do I need to upload an Excel file? No. Paste or type the serial value directly.