If Is Last Page (of Paged Post)

I’m really stuck on this, and hope someone can help.

With multipage posts (via <–nextpage–>), I need to determine via PHP if the current page is the LAST page. I know how to call $multipage (to handle single-page posts as an else, for example), but I don’t know exactly how to determine if the current page number equals the total number of pages.

I’m betting (hoping) this is a simple little task for you PHP gurus out there. Could someone please help me with the code? I’m trying to use this in a new plugin.

Thank you!