Open the About dialog box in any Office program.  Near the top, you'll find the build number of the program you're using.

If you are using Office 2003, you'll probably see something like 11.5608.5606.  If you are using Office 12, you might see something like 12.0.3417.1005.  In earlier versions, you'll see something similar.

While these numbers may look like unintelligible garbage, in reality they can be used to tell interesting information about the version of Office you're using.


In Office 2003, the "11" that precedes the build number is simply to denote that Office 2003 was version 11 of Office.  Similarly, the 12 in Office "12" means... well, you get it.  Office XP was version 10, Office 2000 was version 9, Office 97 was version 8.  You get the idea.

The most interesting thing to watch for is the first 4-digit number you encounter.  In the examples above, 5608 and 3417.  These are what we refer to as the "build number."  Every few days during the development cycle, we compile all of the code in Office and turn it into a "build": essentially an installable version of all the work everyone's done up until that point.  Eventually, a build becomes "final" and that is the one that ends up on CDs and in the store.

The 4-digit build number is actually an encoded date which allows you tell when a build was born.  The algorithm works like this:

  • Take the year in which a project started.  For Office "12", that was 2003.
  • Call January of that year "Month 1."
  • The first two digits of the build number are the number of months since "Month 1."
  • The last two digits are the day of that month.

So, if you have build 3417, you would do the following math: "Month 1" was January 2003.  "Month 13" was January 2004.  "Month 25" was January 2005.  Therefore, "Month 34" would be October 2005.

3417 = October 17, 2005, which was the date on which Office 12 build 3417 started.

For Office 2003 and XP both, "Month 1" was January 2000.  So, the final build of Office 2003, 5608, was made on August 8, 2003.

If you look at Office 2003 build numbers, you will see two four-digit numbers, separated by a period.  The first of the two numbers represents the build number for the program you're using (such as Outlook.)  The second of the two numbers represents the build number for the core Office shared library (called MSO), which is shared by all programs.

The Office 12 dialog boxes actually show the application and MSO build numbers separately--they're both even labeled so that it's easy to tell them apart.  The Office 12-style build numbers (12.0.3417.1005) reveal another internal artifact of the way we do builds--something we call "dot builds."

Sometimes it's necessary to have two kinds of builds going on at once within the Office team.  Recently, our build lab has been making both "Beta 1" builds and "Beta 2" builds.  In order to ship a stable Beta 1, we have slowed the rate of code changes dramatically and concentrated on just crucial bug fixes.  At the same time, we need a place to check in all of the other work people are doing for Beta 2--but we can't have those changes coming in and wrecking the stability of Beta 1 at the last minute.

The solution?  The build lab makes two kinds of builds at once.  A specific build number is chosen, and that build "becomes" Beta 1.  In this case, 3417.  That doesn't mean that Beta 1 is done however.  As bug fixes are checked in, we make new versions of the 3417 build, each one with an increasing number as a suffix, separated by a period.  (A so-called "dot" build.)  So there would be a 3417.1, 3417.2, 3417.3, and so on until Beta 1 is ready to ship.  Subtract 1000 from the second 4-digit number in the About box to find the "dot build" number.  In the above example, 3417.1005 is the 5th "dot" build of our Beta 1 branch.

At the same time, the build lab continues to churn out Beta 2 builds on the normal daily schedule: 3423, 3425, etc.  So, internally, we can tell which build is which kind by the number it has.

Last point: once a product ships, the rules for build numbers become even more complicated and different.  So, if you have Service Pack 2 for Office 2003, you might see a nonsensical number like 6552 or something.  Don't worry about it, it's not tied directly to a date in the same way anymore.

Armed with this knowledge, you're ready to amaze the world with your secret ability to decode Office build numbers.