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Excel Serial Date Converter: Serial Number to Date and Back

This free tool converts Excel serial numbers into dates and dates into serial numbers. It supports both the 1900 date system used on Windows and the 1904 system used on old Mac files, and handles the time as a fraction.

By Debmedia Technologies LLP · Kolkata, India · Updated

What Is It and When Do You Need It?

Spreadsheets, CSV exports and databases often show dates as plain numbers. This tool turns the number back into a date you can read.

Type the serial number, or a date to get its serial number.

How to Use This Tool

  1. Enter or paste your input in the box or boxes above.
  2. Choose the options, if there are any.
  3. Press the button to run the tool.
  4. Read the result and use the copy button where one is shown.

How the Calculation Works

In the 1900 system serial 1 is 1 January 1900, and one day is added per step, with the leap year bug adding a phantom day after 28 February 1900. So for serials of 61 and above the date is 30 December 1899 plus the serial. In the 1904 system serial 0 is 1 January 1904. The part after the decimal point is the fraction of a 24 hour day.

Worked Example

45000 is 15 March 2023. The date 1 January 2024 is serial 45292. A serial of 45000.5 adds 12:00 noon.

Common Uses

  • Cleaning CSV files.
  • Fixing import errors.
  • Working with data exports.
  • Writing formulas.

Tips and Common Mistakes

  • Serial numbers under 1 are only times.
  • Check the date system if dates are off by four years.
  • Serial 60 is a date that never existed.
  • Check the first result against a case you already know, so you can trust the tool for the rest.
  • Nothing you type leaves your device. The work is done by your browser, so it also works with a slow connection once the page has loaded.

Next, you may need the Unix timestamp converter, Julian date converter, day of the week calculator, date difference calculator.

Everything runs in your browser. Nothing you type is uploaded, stored or sent to any outside service.

Frequently Asked Questions

A number that counts days since a start date. The whole part is the day and the decimal part is the time of day.
Excel treats 1900 as a leap year, so serial 60 is the non-existent date 29 February 1900. Dates from 1 March 1900 onward are right.
Early Mac versions of Excel started counting from 1 January 1904. The setting is stored in the workbook.
The cell is formatted as General or Number. Format it as a date and Excel shows the date.

Disclaimer: results are calculated in your browser from the numbers you enter. Check important results before you rely on them for money, health, safety or legal decisions.