I'm thinking of paying a professional proofreader to go through my PhD thesis, but not sure when would be the best time. Before I submit, or after the viva and any corrections I have to make for the final version? It's a lot of money and I don't think I could afford to have it proofread more than once. What are everyone's thoughts on this?

I would say before the viva if you are convinced that your thesis's content is good and stands to scrutiny. If you are in doubt about the content then after.

Definitely before. I read an article the other day that said that one of the things that examiners judge the thesis by is the readability/grammar side of things. Re your concern about needing it proofread twice (if you did get it done before the viva) - this wouldn't be necessary. You can simply highlight your corrections and proofread those parts yourself (or have someone else do it).

That said, as a native English speaker, I wouldn't invest in a professional proofreading service unless you are really concerned about it. I would just proofread it myself and have kind friends proofread parts of it for me.

I also agree with AlphaOmega. If you seriously think you are going to have to re-write your thesis or large parts of it, then having it proofread after would make sense. But why would you be submitting if you honestly felt that way about it?

Thanks for the replies. That makes a lot of sense and I will probably have it proofread before, or as you suggest get some of my kind friends to help out. :)

Proofreading is definitely important before you face the viva for your research. Human error can never be avoided, hence it is always better to proofread the document once drafted. Proofreading the document is the best option. However, due to lack of time, we might need to avail professional proofreading and consequent editing service. The professional proofreading and editing service might also be helpful in finding the errors which our eyes have overlooked. Hence it is highly recommended. If you're concerned about the charges its always better to get it verified from your peers or friends and then go for professionals. Here is the link to professional proofreader service -