The deadline has been extended from 30 November 2020 to 28 February 2021.
The Revenue Service says it recognises the impact the pandemic has caused many islanders and businesses.
"We know it’s been a really turbulent year for so many people in so many ways. While of course it is important that people do fill out their returns, we understand that it is one more bit of ‘life laundry’ to have to worry about so by extending the deadline we’re hopefully giving people a little bit more breathing room." - Nicky Forshaw, Director of the Revenue Service.
People who fail to get their paperwork in by the new deadline will face penalties.
The change will mean 2020 returns will not be available until later, and a new date will be announced later this year.
Islanders are encouraged to fill out their returns online.