While the balance sheet approach has increased the focus on position data, differences in valuation practices for foreign direct investment (FDI) make cross‐country comparisons difficult. To enhance comparability, the IMF's Balance of Payments and International Investment Position Manual, sixth edition, which some countries have already implemented and others will implement in the coming years, recommends seven methods for valuation of unlisted FDI. This paper demonstrates that both the valuation method and simple differences in estimation techniques can fundamentally change a country's financial balance sheet. Using Denmark as an illustration, unlisted FDI equity liabilities vary from 22 to 156 percent of GDP when applying different estimation techniques, but just one valuation method, price to earnings. These measurement uncertainties can lead to important misunderstandings and affect policy recommendations, thus pointing to the need for further international harmonization. While the results are presented in an FDI context, the uncertainties also apply to other macroeconomic datasets, including national accounts statistics.