Nobody wants to send an email to their PhD supervisor saying they've achieved nothing in the last three months. The more time passes, though, the harder it becomes.

An example:

Let's say, for whatever reason, you are unable to work for a whole month. You have two options with regards to what you tell your supervisor:

• You can just tell them you have fallen behind, or...
• You can say nothing and wait until you've caught up with where you should be.

The second option avoids a potentially awkward conversation, but it also places you under a much higher burden of expectation.

Another month goes by, but you haven't yet caught up with where you should have been after that first month (perhaps because you under-estimated how long that piece of work would take). It's now been two months, so you want to produce even more before you say anything.

The more time passes, and the more you feel you should have produced, the harder it gets to reach out. You avoid being reprimanded, but you also become more and more isolated.

By far, the most common cause of PhD failure (or extreme difficulty) I have seen is isolation and a lack of feedback from other academics. So if you're in this situation, don't wait to re-establish contact. Do it today.

I know it's been a long time since I sent an update. I've fallen behind quite a bit but am doing my best to get back on track. Right now I'm working on ..., but am not sure how to ...

Keep it brief, don't make excuses, and if you're having technical problems, ask for guidance.

It's so easily avoidable...

I'd recommend emailing your supervisor every two weeks with brief updates, no matter how well or badly it's going, saying what you've done, what you're working on, what you plan to do next. For example;

"Just a quick update: I'm still working on the analysis of ..., which is taking a little longer than expected as I'm having to learn (technique) as I go. Realistically, this is probably going to take another week or two, and the next step will be to..."

It only takes 30 seconds of their time, and it ensures that they always know (and you have a record to prove that they know) what stage your project is at.

Don't try to hide like a kid who hasn't done their homework. Be professional, be honest and communicate.