So if you get a range from the institution like 400-500 words, you need to write at least 400 words.
If you write less, it will come across like you have nothing to say, which is not an impression you want to give.
However, I advise against exceeding the word limit unless it's explicitly allowed for a few reasons: If you can truly get your point across well beneath the word limit, it's probably fine.
Brevity is not necessarily a bad thing in writing just so long as you are clear, cogent, and communicate what you want to.
College essays are usually pretty short: between 200 and 650 words.
Admissions officers have to read a lot of them, after all! What if your poignant anecdote is just 10 words too long—or 100 too short?
We are particularly interested in your ability to construct a tightly reasoned, persuasive argument that calls upon literary, sociological or historical evidence.
You should NOT submit a laboratory report, journal entry, creative writing sample or in-class essay." While there is usually no word limit per se, colleges sometimes provide a general page guideline for a writing samples.
So for a 500-word limit essay, try to get to somewhere between 450-500 words. College essay prompts usually provide the word limit right in the prompt or in the instructions.
For example, the University of Illinois says: "Explain your interest in the major you selected and describe how you have recently explored or developed this interest inside and/or outside the classroom.