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 ( α ), the model-based upper-tail parameter ( ω ), and their interval ( δ = ω - α ) are estimated annually from the 1990s onward. Across countries, α increases steadily, whereas ω declines or stabilizes and δ 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 ω ≈ 120 years and α ≈ 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.