HM Revenue & Customs (HMRC) has issued a reminder to anyone who hasn’t yet submitted their 2008-09 Self Assessment tax return.

The reminder stresses that the 31st October deadline for paper returns has now passed, which means anyone yet to file must do soonline by the 31st January deadline. HMRC warns that if you submit a paper return after 31st October, or you file online after 31st January, you could receive a £100 penalty.

HMRC are expecting more than 9.5m Self Assessment returns this year. Around 5.8m people filed online last year, up from 3.8m the previous year – an increase of over 50%.

If you’re a first-time Self Assessment filer, or you are new to online filing, you’ll first need to register for HMRC’s Self Assessment Online service first.

Registering is simple – visit the HMRC website and click “Register for Self Assessment Online”. Once you’ve registered, an activation code will be sent to you in the post.

Note: It can take up to seven days for your activation code to arrive, so register as soon as possible.

The main benefit of filing online is that your tax is calculated automatically, you get an online acknowledgement once you’ve filed, and it’s processed faster, so any money you’re owed is repaid more quickly.

HMRC’s Sarah Walker said:

“If you haven’t yet sent us your 2008-09 tax return, don’t forget, it must be sent online before 31 January. And if you haven’t filed online before, make sure you allow plenty of time to complete the registration process – that way, you’ll avoid a last-minute rush at the end of January.”

And don’t forget, 31 January 2010 is also the deadline for paying any tax you owe for the 2008/09 tax year.