You will receive your pre-completed tax return in March or April. Check your tax return; if it is complete and accurate you need take no further action. If you do need to make changes, you can do so online.
The deadline for submitting corrections is
Checking your Tax Return
Check that the data on your tax return is complete and accurate. If it is, you need take no further action. If you make no corrections, you are deemed to have submitted your tax return and approved it as is.
Making necessary corrections
Tax Return on the Web (tax.fi/taxreturn)
Go to online service
The e-Service has opened 8.3.2018 for the taxpayers whose personal deadline date for filing a tax return is 3.4.2018 (self-employed traders and self-employed professionals). For other taxpayers, the opening date is at the end of March.
The service will guide you step by step through the process. If you choose to use the online service do not send back the tax return or submit any supporting documentation. You will need your personal e-banking identifiers to log in.The service lets you access only your own tax return, not anyone else's.
You may choose to enter your corrections on your printed pre-completed return (and any enclosures where appropriate) and send them to the tax administration. To download enclosures, visit tax.fi/forms or ask for paper copies at your local tax office.
If you opt for paper filing, use the self-addressed, prepaid envelope.
Extending the deadline
If there are valid grounds for doing so, the Tax Administration may grant an extension of the deadline. Any request for such an extension must be submitted well in advance.