Excel Date Converter

How to use

1. 1Pick the spreadsheet system at the top: Excel 1900 for most Windows workbooks, Excel 1904 for older Mac files, or Google Sheets and LibreOffice Calc.
2. 2Choose a direction: Serial number to date (decode a number from a CSV export or formula) or Date to serial number (find the Excel-compatible serial for a calendar date).
3. 3Type or paste the value. Integer serials give you the date alone; serials with a decimal also decode the time of day. Dates accept ISO 8601 like 2024-12-31 or 2024-12-31T08:30.
4. 4Read the result panel for the ISO date, US and EU formats, long date with weekday, day of year, Unix timestamp, and whole-day and fraction parts so the math is verifiable.
5. 5Use the copy buttons to grab the serial, the ISO date, or a full summary block ready to paste into a ticket, a code comment, or another spreadsheet.

About this tool

Excel Date Converter is a browser-based tool that converts between Excel serial date numbers and human readable calendar dates in both directions, for all three of the conventions real spreadsheets use. Pick Excel 1900 (the default on Windows, where serial 1 is January 1, 1900), Excel 1904 (the older Mac system that anchors serial 0 to January 1, 1904), or Google Sheets and LibreOffice Calc (which anchor serial 0 to December 30, 1899), and the math switches to match. In serial-to-date mode, paste a number you found in a CSV export, a CSV pasted into a Google Doc, or a cell formula and get back the exact calendar date Excel points to, including the weekday, ISO 8601 representation, US (MM/DD/YYYY) and EU (DD/MM/YYYY) formats, the day of the year, and the Unix timestamp for cross-checking with other systems. The fractional part of the serial is decoded into hours, minutes, and seconds, so a value like 45631.5 resolves to noon on its date. In date-to-serial mode, type any ISO 8601 date (with or without time) and get the matching serial number, the whole-day part, and the fractional time component, ready to paste back into a spreadsheet cell formatted as a number. The tool faithfully reproduces the Excel 1900 leap year bug (Excel treats 1900 as a leap year even though it is not, so serial 60 maps to the phantom date February 29, 1900, and every later date is shifted by one against a true Gregorian count). A live snapshot at the bottom shows the serial number for today in all three systems, which is the answer to the common search query 'what is today as an Excel serial number'. Useful when you are auditing a spreadsheet export, decoding raw date numbers in a CSV, building a formula that needs a literal date constant, debugging a date that exported as 45631 instead of a real date, migrating data from Excel into a database with a different epoch, or just satisfying a curious 'what date is Excel serial 25569?'. All parsing, epoch math, and rendering happens locally in your browser, so the numbers and dates you paste here never leave your device.

Free to use. Works in your browser. No signup, no login.