When is it correct to use contractions in formal writing?
Using contractions on your IELTS or TOEFL writing examStudents often ask us here at Scott's English Success! when they should use contractions (I'll, She's, They'd) on their written exams.
The short answer is, "Never."
While contractions are very common, and even expected in oral English, and should be used during your oral exam, you should not use contractions when answering questions on the written exams.
Writing the two words instead of the contraction shows that the writer knows the difference between spoken English and written English.
There is one exception, 'reported speech', if you are quoting someone and need to quote the person correctly. So, writing "The farmer said, 'I'll need to plow that field today'. " is correct.