Sustaining Growth Under Demographic Decline: A Minimum AI Investment Threshold for OECD Economies

Population aging weakens the research base for growth in Organisation for Economic Co-operation and Development (OECD) economies. This paper develops a balanced-growth benchmark with semi-endogenous knowledge production, human-capital deepening, and artificial intelligence (AI) research capital to derive in closed form the minimum AI-investment share consistent with non-negative per capita growth. Calibrated to an illustrative 15-country OECD sample spanning contrasting demographic regimes and gross expenditure on research and development (GERD)-intensity profiles, using United Nations World Population Prospects 2024 and OECD Main Science and Technology Indicators data, the formula yields midpoint thresholds of 0.236–0.275% of gross domestic product (GDP) when 10% of GERD is assumed to be AI-designated. The midpoint normalization is anchored to the best currently available OECD/European Commission (EC) measurement evidence, which places the AI-designated share of aggregate research and development (R&D) at 8.8% for the EU27, 9.9% for the United States, and 7.9% for Japan—all within the 5–15% window used here. Although this range is narrow in GDP-point terms, it implies research requirements from about 5–7% of GERD in South Korea and the United States to about 18–20% in Italy, Poland, and Spain. The common normalization shifts levels but not the cross-country ranking. These results favor demographically adjusted, country-specific AI-investment benchmarks over an OECD-wide target and imply that migration and research-base expansion can partly substitute for higher AI spending in high-pressure economies.