It is always scary pushing the submit button on your self-assessment. Even for veteran contractors, sending the final document can be unnerving because traditionally, HMRC doesn’t have much sympathy for mistakes.
penalties Articles
If you have missed the 31st January deadline don't panic too much.
If you are more than a day late then you are already be subject to a £100 fine.
Some potentially good news for contractors who operate through their own limited company is that HMRC have relaxed their deadline for Limited Companies (with less than 50 employees) that are adjudged to be late filing their monthly PAYE returns and hence liable for a penalty.