Spouses are again able to give their full matrimonial capital to the longest living spouse, without their children being taxed again for the same portion of the estate: the Flemish tax authorities (VlaBel) have approved the "clause of optional attribution under burden" (also known as the "Casman clause") in matrimonial contracts.

Clauses of total or optional attribution under burden are clauses in a matrimonial contract which allocate to the longest living spouse the full ownership of all or specific goods of the matrimonial capital when he or she is widowed.

Such a provision provides more comfort for the longest living spouse than the statutory legal provision. Under such a clause, the longest living spouse is given full ownership of (specific) jointly owned matrimonial goods (in excess of "his" half to which he is entitled by law) instead of the usufruct on half of the jointly owned goods as provided for by law (in excess of "his" half to which he is entitled by law).

A classic clause of total attribution does come at a tax price, however. The surviving spouse will be taxed on the part that exceeds half of the jointly owned matrimonial goods. Once the surviving spouse dies, the children will be taxed again on the full value of all the matrimonial goods their parents jointly owned. Consequently, when looking at the taxation after the passing away of both spouses, half of the jointly owned matrimonial goods will have been taxed twice.

In order to eliminate this problem, practitioners introduced the "clause of total attribution under burden", a technique used in the Netherlands for quite some time now. The essence of this clause is that the surviving spouse receives all or part of the jointly owned matrimonial goods in full ownership, but has to accept a burden, consisting of a debt to the estate equalling the value of the goods received in excess of half of the jointly owned matrimonial goods. The repayment of this debt will be postponed until the passing away of the surviving spouse. Often, interest is also set on the debt.

When the first spouse dies, his or her children will be taxed on the value of the claim representing the burden. When the surviving spouse passes away, the debt is considered as a liability of the legacy (provided that no premature repayment has occurred), allowing it to be deducted from the taxable amount of the legacy. This way, the children will not be taxed twice on the relevant matrimonial capital of their parents.

The tax consequences of such clauses were questioned by the tax authorities in 2013. The federal ruling commission labelled the use of clauses of total attribution as tax abuse. This decision caused a great deal of uncertainty and was heavily criticised by legal scholars. In 2015, the Flemish tax authorities (VlaBel) announced that, for the calculation of inheritance tax, they too would not take into account any burden/claim in connection with a clause of total attribution.

The Flemish tax authorities have recently changed their point of view. It is now explicitly accepted that the burden/debt comes into existence when the first spouse dies. Hence, the surviving spouse will not be taxed on the part that exceeds half of the jointly owned matrimonial goods. The children will have to pay inheritance tax on the value of the burden/debt in bare ownership.

When the remaining spouse dies, it is accepted by VlaBel that the nominal value of the burden/debt will be deducted from the part that is taxable in the hands of the children in the second legacy. This way, no double taxation occurs. If interest on the burden/debt has been stipulated, the interest amount will not (to the disadvantage of the children) be deducted from the taxable amount in the second legacy.

This vision of VlaBel is not legally convincing, but it is rather a practical solution which aims to avoid double taxation of the heirs.
Either way, the approval of the clause of optional attribution under burden is a step in the right direction, and consequently the use of such a clause can be advised in certain scenarios.