Global evidence for bounded human lifespan growth

Is there a limit to human lifespan? We examine upper-tail lifespan dynamics in 46 countries using reliable period life-table data. The characteristic life ( $\alpha$ ), the model-based upper-tail parameter ( $\omega$ ), and their interval ( $\delta =\omega -\alpha$ ) are estimated annually from the 1990s onward. Across countries, $\alpha$ increases steadily, whereas $\omega$ declines or stabilizes and $\delta$ narrows, a pattern consistent with postponed and increasingly concentrated late-life mortality rather than unlimited upper-tail expansion. Under the baseline $L=120$ projection model, both females and males approach $\omega \approx 120$ years and $\alpha \approx 103.5$ years by 2100. Sensitivity analyses show that the inferred asymptotic boundary is model-dependent, so the projected value near 120 years should be interpreted as a mathematical upper-tail estimate rather than a definitive biological maximum. These findings are consistent with, but do not establish, an increasingly bounded upper-tail survival regime within the present demographic and modeling framework.