An English-language version of this guidance is not yet available but will be released soon. For more information, read the Tax Administration's bulletin What you need to know to become an independent taxi driver? (in Finnish only)
The income you receive from the provision of passenger transportation on a crowdsourcing basis (Crowd-based passenger transport service e.g. Uber) is regarded as taxable earned income.
You can deduct the expenses that relate to the operation of the services i.e. deduct the Uber-related part of your car's running costs. The deductible amount is the actual costs. If no other calculation of costs is available, the car's running costs can be estimated under the Tax Administration's official guidelines (called "the guidelines for harmonization"–yhtenäistämisohje) that is updated every year. Under the official guidelines, the size of the deduction is €0.24 per kilometre (for the 2017 taxable year).
Crowd-based passenger transport is treated as a service you provide in a small scale, i.e. not as your principal occupation. For this reason, its costs can only be deducted from the income you receive from passengers. This also means that if your costs are higher than that income, you are not entitled to tax deductions for the loss.
How to file online
On your tax return: submit the income you have received under "Other earned income", and the paid expenses under "Expenses for the production of income". Fill in the Additional Information field to provide a more detailed account of the income.
On your tax card: submit the amount of your net income – i.e. what is left after you deduct the expenses – under "Business income subject to prepayments" → Earned income from a business source.