In this case, “overloaded” is synonymous with “deadlines will be missed”. “Overloaded” does not mean “I’m extra stressed this week”. So with that being said…
Telling your boss you are overloaded can bring with it negative connotations such as: you are bad at prioritizing, bad at time management, or just slow. In other words, their first reaction is likely to be that you’re just complaining and not stating a fact.
A more tactful way is to do as I said above. Create a list of all your major tasks and prioritize them. Then go to your manager and ask them to verify the priorities as you have outlined without saying that you are overloaded.
This lets them see on paper that you have a lot on your plate. This also lets them know you are thinking ahead and that you are practicing prioritization skills. This also lets them take some responsibility for when you miss a deadline on a task because you BOTH agreed it was a lower priority. In doing this, you avoid the questions and criticism for missing a deadline. Plus, your manager now serves as a first line defense. They will be ready to defend you because they know why you missed a deadline and they were part of the process that led to that happening.
I speak from experience. A year ago this burned me. I missed a deadline because I never conveyed how taking on a new higher priority task forced me to postpone work on another major project. When the deadline came, hell rained down on me because I did not convey to my superiors that I had to keep pushing my project out to work on higher priority items. They were blindsided when I missed my deadline and I was blindsided by how disappointed they were with me.
The real LPT here is: as your priorities change, make sure your boss knows how that impacts your other tasks and the deadlines associated with them.
Update: I didn’t expect this to resonate like it did! I’m glad it’s a useful LPT to so many. To clarify, I’m most certainly not advocating you abuse this. As with anything, this is a useful tool when used smartly. And obviously this is under the assumption your manager is at least decent at what they do and care about their subordinates.
