You're finished when you say you're finished.
That's it. Pretty easy, no? Ever since slavery was abolished, no one can force you to work. The technical term is a "contract of personal service" and that's what a writing contract is: you're not allowed to subcontract the job, it's you who has to do it yourself.
But it's not that simple. The issue isn't in deciding when you're done, the issue is in determining what are the consequences.
Let's start with an easy scenario: your contract says you'll deliver a 35,000-word manuscript and you deliver 25,000. You haven't performed under the contract. Clearly, you haven't performed. We'll discuss in more detail in a future post what that means, but for now you should assume you'll be asked to give back your advances and the publisher won't accept the manuscript. But if you really don't want to write anything more, you don't have to.
But what if you've delivered 35,000 words? Then you've done what the contract says. And so from a purely technical perspective, you've performed your obligations under the contract. If your publisher tries to send the manuscript back saying you haven't performed, they can't raise word count as a reason.
Now let's add a couple of wrinkles. If the contract says 35,000-40,000 words and you turn in 34,000, you still haven't performed. Same thing for 34,999. Now the question arises: is this really a fundamental breach allowing your publisher to say that they will reject the manuscript? If this happened to a client of mine, I'd argue that this is technical performance: in the course of edits it may be the case that the publisher converts the manuscript into 35,000 words all by itself: removing contractions, fixing grammatical errors, etc. (which itself can become "et cetera" or "and so on")... But make your life easier and find somewhere to add enough words to get you to your minimum. It's tedious, but it removes an issue that doesn't have to be there.
How about if you turn in 41,000 words? Same thing, except it makes my Spidey sense tingle a bit more. Sure, your editor may cut out enough words that your manuscript ends up being in the 35,000-40,000 word window. But if they don't, then you may have a problem, and maybe they just don't want to do the work at all and they'll reject - in some types of fiction as well as in non-fiction, that might be a risk. Better not to take it. And here's some tips for that...
1. Where possible, don't commit to a word count. Try to get something like "a book-length manuscript" or "a feature-length article". That can raise its own issues in this era of Kindle Singles and the like, but at least it takes away the objective and artificial measure.
2. If that doesn't work, and in cases like magazine articles it probably won't, try getting something like "approximately" put into the word count, so that you would really have to miss the target by a lot in order to be in breach.
3. And if you can't do either of those, learn where the Word Count feature is in your word processor and make it your friend.
It's never that easy though. What happens when the publisher doesn't like the content of what you wrote? That'll be the topic of tomorrow's post...