Center for Open Science (2025). In 2017, Finland introduced a partial old-age pension scheme, allowing individuals to claim either 25 or 50 percent of their old-age pension after turning 61, irrespective of their employment status. Claiming a partial pension before the statutory retirement age results in a permanent reduction of the full old-age pension. Due to the rapid rise in consumer prices in 2022, individuals who claimed their pension before the end of 2022 benefited from a three-percentage points higher index adjustment in 2023, resulting in a permanently higher pension compared to those who claimed their pension in early 2023. In this study, we assess the causal effect of the financial incentive arising from the exceptional index adjustment on pension take-up using regression discontinuity design and full population register data. We also analyse differences in responses by socioeconomic status and gender. The extraordinary pension index adjustment increased the probability of claiming the partial old-age pension in the first month after becoming eligible for it by around 8 percentage points, or around 80 per cent. The effect is explained by individuals claiming a pension sooner than they would have in the absence of the exceptional index adjustment. Individuals with a higher pension accrual, higher earnings, or with upper tertiary education were more likely than others to respond to the index adjustment.