Most advice about emailing a professor is about tone. Tone matters far less than two other things: whether you asked before the deadline, and whether the email contains a specific proposal they can answer in one word.
Before beats after, by a lot
The same email sent Tuesday and sent Friday is a different email. Before the deadline you are a student managing their workload, which is a thing instructors like seeing. After, you are a student explaining a missed deadline, which is a category with a lot of unconvincing entries in it.
It is also a practical difference. Before, they can grant an extension. After, many institutions require them to apply the late policy and route anything else through a formal process, so the answer is constrained regardless of how they feel about it.
Make it answerable in one word
An email that ends with a specific proposal can be answered with “yes”. An email that describes a situation puts the work of proposing something back on the person you are asking a favour of.
Hard to answer
Hi Professor, I’ve been really overwhelmed this week with everything going on and I’m struggling to get the lab report finished. I’m sorry, I know it’s due tomorrow. Is there anything I can do?
Answerable in one word
Hi Professor Nadel — I have three deadlines landing Thursday and the lab report is the one I cannot do well in the time. Could I submit it Monday at 5pm instead? The analysis is done; I need the discussion section. Happy to take a late penalty if that is simpler.
The second is not longer or more polished. It is specific: which assignment, why, what is already done, exactly when it would arrive, and an acknowledgement that a penalty is acceptable. That last part removes the awkwardness — you are asking for time, not for the rules to be suspended.
What to leave out
Medical detail you were not asked for. “I have been unwell” is sufficient and appropriate. Anything more usually belongs with a dean or student services, who can grant things an instructor cannot.
A list of your other commitments. One sentence of context helps; a paragraph reads as a case for why their course should come last, which is not the impression you want.
Apology stacked on apology. One is professional. Four reads as anxiety and makes the email harder to reply to, because now they have to reassure you as well as answer you.
The shape that works
Roughly five lines, in this order:
Who you are and which course, if they teach more than one section. They may have three hundred students.
The specific assignment. Name it as it appears in Canvas.
One sentence of why. No more.
Your proposal, with a date and a time. This is the email.
What is already done, if anything is. It is the difference between an extension and a rescue.
If they say no
Take it, submit what you have, and move on. An instructor who declines an extension is usually applying a policy consistently rather than judging you, and arguing converts a neutral interaction into a memorable one in the wrong direction.
A partial submission on time is almost always worth more than a complete one late — and in courses with an automatic missing-submission policy, it is the difference between a mark and a zero.
Related
Worth knowing what a late submission actually costs before you ask — what happens when you submit late covers the policies, and why weeks collapse covers how you ended up here.