Excel Date Converter

Convert Dates and Excel Serial Numbers Without the Guesswork

If you’ve ever wrestled with Excel’s strange way of handling dates—or found yourself puzzled by the numbers behind its date system—you’re in the right place. This converter is built to take the confusion out of turning real-world dates into Excel serial numbers (and back again), while letting you adjust for different systems and time zones along the way.

Why This Converter Exists

Excel doesn’t store dates the way we write them. Instead, it counts days since a fixed point in time: either January 1, 1900 or January 2, 1904, depending on the platform or settings. That means something like 44927 in Excel actually represents January 1, 2023—but only if you’re using the 1900 system. Throw in fractional values for times of day, and it’s easy to get lost.

This tool bridges that gap. Whether you’re debugging a spreadsheet, coordinating across time zones, or trying to make sense of a CSV export, it translates between calendar dates and Excel's behind-the-scenes numbers with clear, readable results.

What You Can Do With It

• Convert a calendar date and time into an Excel serial number (1900 or 1904 system)
• Convert an Excel serial number back into a human-readable date and time
• See detailed breakdowns, including day of the week and time fraction
• Adjust everything based on your time zone
• Toggle between 12-hour and 24-hour time formats

How to Use the Converter

1. Choose What You’re Converting

Right in the middle, you’ll see two options: Date to Excel Serial or Excel Serial to Date. Pick the one that matches what you’re working with.

2. Fill in Your Inputs

If you’re going from a date to Excel:

• Enter a date using the calendar input
• Add a time if needed (defaults to midnight)
• Pick your time zone (UTC is default)
• Select which Excel date system you’re using—1900 for most Windows files, 1904 for older Mac versions

If you’re going from Excel to a date:

• Type in the Excel serial number (can include decimal time fractions)
• Choose the correct date system to match the source file
• Pick the time zone you want the output to show

3. Hit “Convert Excel Date”

The big button in the center does all the work. When you click it, the result appears instantly—no page reload, no waiting.

What the Results Tell You

The main output gives you the exact conversion, but there’s more underneath:

• Date & Time: The full converted value in your selected time zone
• Day of Week: Helpful for cross-checking weekdays
• Days Since Epoch: Raw day count from the system’s starting point
• Time Fraction: A decimal that represents the time of day (e.g., 0.5 = noon)
• Formatted Date: Easy-to-read calendar version
• Both Serial Numbers: You’ll see what the number would be in each date system
• Excel Formula: A ready-made formula you can paste back into your spreadsheet

Live Tools at a Glance

In the side panel, there are a few helpful extras always ticking in real-time:

• Current Time: Shown in your chosen time format
• Current Excel Serial (1900 & 1904): So you can see what “now” looks like as a serial number
• Time Format Toggle: Prefer military time? One click switches to 24-hour display

Advanced Details for Curious Users

Excel’s Two Date Systems

The 1900 system starts counting from Jan 1, 1900—but includes a made-up leap day for compatibility with old software, which can cause slight quirks. The 1904 system starts from Jan 2, 1904, and skips that bug. They’re 1,462 days apart. If you ever import dates between systems and find them mysteriously four years off, that’s why.

Decimal Time Values

Excel stores time as a fraction of the day: 0.25 is 6:00 AM, 0.5 is noon, 0.75 is 6:00 PM. If your serial number includes a decimal, this converter translates it automatically.

Formulas You Can Copy

Every result includes a formula like =TEXT(44927.645833,"mm/dd/yyyy hh:mm:ss") that you can paste into Excel to recreate the date. This makes it easy to check or reuse your conversions.

A Few Things to Keep in Mind

• Excel for Mac now defaults to the 1900 system, but older files might still use 1904
• If you copy serial numbers between systems, expect a 1,462-day shift unless converted
• Serial numbers under 1 either produce errors or dates before Excel’s start date
• Always check which system your spreadsheet is using before converting

Keep Your Dates Straight and Your Sheets Accurate

Whether you're comparing timestamps across systems, debugging spreadsheet exports, or just curious about what Excel's serial numbers really mean, this converter saves time and clears up confusion. It brings structure to a process that’s often full of tiny details—and helps you stay confident when working across platforms, time zones, and Excel quirks.