TL;DR: A married couple in Finland should keep the spouses’ money and property separate.
A common household expenses account is probably fine, as is paying common expenses and personal expenses of the other spouse from one’s own money. Direct transfers of money or other property from one spouse to the other are likely to trigger gift tax, however.
Recently I have studied the law of marriage. As regards to money issues, I was naive to think that I could regard both spouses’ money as common property; in Finland, this is not so.
It is true that when a marriage ends (by death or by divorce), in the absence of specific prior restrictions, both spouses’ net worth is combined and distributed to each spouse (or their inheritors) 50-50. However, this does not say anything about how things are during a marriage.
In a marriage, under Finnish law, money and property held in the name of one spouse is generally the money and property of that spouse, and money and property held in joint ownership is (of course) jointly owned in the proportion specified. Interestingly, a court has held that a spouse transferring money to a joint bank account to which they have unilateral access retains ownership of that money until it is transferred out of their grasp (by being spent, for example); thus, money in that account is separately owned by each spouse to the extent of their net contributions, and no joint ownership is implied.
A spouse in a marriage has, in Finland, the legal duty, to the extent they are able, to take part in the common household economy and in fulfilling both spouses’ common and individual needs (see the Marriage Act, Section 46, Paragraph 1). This seems to mean that both spouses must take part in household chores and contribute what they can from personal income and assets to the family economy: the household must be maintained, and its needs must be met by appropriate purchases. Additionally, each spouse has a duty, in addition to meeting their own needs, to contribute in the fulfilling the needs of the other spouse. In many cases, this means that the spouse who makes more money spends money not only on their own needs and on common needs but also on the needs on the other spouse.
This duty does not mean, however, that a spouse can simply give money to the other spouse without tax effects. The gift tax enters the picture as soon as one spouse gives money or other assets freely to the other spouse. Just the intention of covering marital duties does not exempt the transfer from tax. What is needed is that the recipient must not be able to spend the money on other things. Thus, one can pay a grocery bill, but one cannot (without demanding an accounting) give money to pay for the groceries. As little as 150 euros per month is enough to trigger the tax within three years. See the inheritance and gift tax act Sections 19 and 19a.
It seems safe to use a joint debit card to be used for household and private expenses, so long as both spouses demand an accounting from the other on its use. The court decision I mentioned above seems to mean that simply putting money on such an account is not a taxable gift, and so long as both spouses actually account for their use of the joint card, their use of it in excess of their own contribution should be the exploitation of an untaxable marital duty. I am not certain of this interpretation, however.
Accumulating assets over what a spouse can afford by themself is very likely to involve taxable gifts, however. For example, if the couple uses the savings and future earnings of the higher earning spouse to buy a house under 50-50 joint ownership, this is very likely a taxable gift to the other spouse. Similarly, using both spouses’ income to accumulate retirement savings in one spouse’s name might be seen as a taxable gift (though it might be possible to explain it to the tax office as a joint savings in truth). Instead, both spouses should save independently, and at retirement, the higher savings of one can be used to discharge the marital duty to the other spouse.
My conclusion is that married spouses in Finland should keep their finances separate as much as possible. Avoid common bank accounts (apart possibly from household and private needs spending accounts), avoid joint savings. Undivisible property, like apartments and houses, should be listed in the ownership proportions corresponding to actual contributions: if one contributes 100 000 euros and the other 10 000 euros, the proportion should be listed as 90–10. If you do all this, you are unlikely to accidentally breach the gift tax act.
If you have a different opinion, or if you want to discuss this, feel free to use the comment box below. I ask that you substantiate any factual or legal propositions by reliable sources, however.