For a correct application of tax laws, it is centralto know at what time or period the conditions of each case are to be tested against the respective tax rule. For example, in many questions, the conditions at the time of the transaction are decisive, but not seldom the tax rules take aim at the conditions at the end of the year – or someother time or period. It is also important to know what significance should be given to events after this time or period, not least when the income declaration is made and assessed. Here, these partly overlooked questions are presentedand analyzed from the Swedish, Norwegian and Finnish income tax-perspectives.