Key legal question
Whether Aargau had to account for post-purchase maintenance costs incurred on the Zug property in the interim tax assessment.
Extracted holding
Yes. The domicile canton had to assume the non-offsettable excess maintenance costs in the inter-cantonal allocation, just as it had to assume the debt interest excess.
Extracted reasoning
To avoid prohibited intercantonal double taxation, the system of separate cantonal taxation must be coordinated so that the taxpayer is not taxed on more than total net income. Interim reassessment triggered by acquisition of an out-of-canton property must also adjust for clearly identifiable additional investments with deductible maintenance components.