Is a limit to the median length of human life imminent?

Human life length tripled in historical times. To examine whether an end to increases in life length is imminent, we computed the median life length and the remaining life expectancy for 6,560 life tables from 1800 to 2008. Within almost all intervals of 20 years, for almost all countries, as median life length increased, the remaining life expectancy at the median life length decreased linearly. This empirical pattern in life tables has not been previously observed. The slope and intercept of this linear relation differed among countries in a given time interval and among time intervals for a given country. This linear relation suggested a hypothetical, easily calculated index of maximal median life length (MMLL) for a given country and time interval, namely, the median life length, according to this decreasing linear relation, at which the remaining life expectancy is zero. In successive 20-year time intervals starting from 1800-1819, the largest value (over all countries, within a given 20-year interval of observation) of this MMLL increased by more than one year of life per year of calendar time. There was no sign of a decreasing rate of increase, suggesting that a limit on median life length is not imminent.