Long-term rate
\ˈlɔŋˈtɜrm\ \reɪt\
A rate of longevity improvement used in some projection models to reflect a long-term sustainable rate of reduction (improvement) to mortality rates.
Usually set using expert judgement with reference to long-term historical longevity trends and effects on longevity (often focusing on medical advances). When using a long-term rate, an age is often chosen where this rate will reduce to zero, reflecting either the belief that mortality rates at the oldest ages will not change at the same rate as at younger ages, or even that there is a biological limit on life.