This formula uses the MATCH function in approximate match mode to locate the last numeric value in a range. Approximate match enabled by setting by the 3rd argument in MATCH to 1, or omitting this argument, which defaults to 1.
The lookup value is a so-called "big number" (sometimes abbreviated "bignum") which is intentionally larger than any value that will appear in the range.
The result is that MATCH will "step back" to the last numeric value in the range, and return that position.
Note: this approach works fine with empty cells in the range, but is not reliable with mixed data that includes both numbers and text.
The biggest number Excel can handle is 9.99999999999999E+307.
When using MATCH this way, you can use any large number that is guaranteed to be larger than any value in the range, for example:
=MATCH(1E+06,range) // 1 million =MATCH(1E+09,range) // 1 billion =MATCH(1E+12,range) // 1 trillion
The advantage to using 9.99E+307 or similar, is that it's (1) a huge number and (2) recognizable as a placeholder for a "big number". You'll see it used in various advanced Excel formulas.
You can use this formula to create a dynamic range with other functions like INDEX and OFFSET. See links below for examples and explanation:
Inspiration for this article came from Mike Girvin's excellent book Control + Shift + Enter, where Mike explains the concept of "last relative position".