Do I still need to file even if I don't owe any tax?

Yes. If HMRC has asked you to file or you meet the criteria, the return is required regardless of whether you owe anything. This catches a lot of people out — especially first-time filers who assume no tax means no return. The £100 automatic late penalty applies from the day after the deadline, whether you owe tax or not. Filing on time, even with a nil bill, avoids penalties and keeps your record clean with HMRC.