Pay an overdue back tax according to the instructions given on your summaryTax Administration Bulletin, 1/2/2019
If you did not pay the back taxes that fell due on 3 December 2018, you will receive a reminder letter as part of your summary. Summaries of tax payment status are shown in MyTax (tax.fi/mytax) 1 January 2019 and they are also sent to taxpayers by post a few days later.
If you have activated suomi.fi/messages, you will receive the summary in MyTax only. To log in to MyTax, you can use your personal online banking codes or a mobile certificate.
You must pay interest up to the actual date of payment
Pay the back taxes by using the payment information in the reminder. The due date is 22 January 2019 as stated on the reminder. Late-payment calculations on summaries are made with an interest period that reaches up to the next general due date. If you pay before the due date, calculate the correct amount of late-payment interest in MyTax or by using the interest calculator (vero.fi/korkolaskuri) (in Finnish and Swedish). Alternatively, you can use MyTax to make your payment online. In this case, the correct amount of interest is included automatically.
Depending on your tax debt status, you may receive payment reminders 1 to 3 times in your summaries before the Tax Administration transfers your unpaid back taxes to the enforcement office for recovery. You will always receive a notification in your summary before the Tax Administration does that. If you encounter financial difficulties, you also have the option to ask for a payment arrangement in MyTax.
See the guidance:
Note: if you had paid your back tax at the end of the month, just before the Tax Administration generates the taxpayers’ summaries, there has not been enough time for the payment to be recorded. If you had already paid the tax, you can disregard the reminder included in your summary.