Definition
A mortality improvement scale is a schedule of assumed year-over-year mortality decline at each age, applied to a base mortality table to project how the table's rates are expected to evolve in future calendar years.
Why it matters
Mortality has been improving over time — at most ages, for most US population subgroups — for more than a century. A mortality table built on a single calendar year captures one moment in this trend; a mortality improvement scale describes how the trend is expected to continue. Naming the scale in use, and the magnitude of improvement it assumes, makes visible an assumption that is decisive in any forward-looking actuarial calculation.
How it works
A mortality improvement scale specifies, at each age, the rate at which mortality at that age is assumed to decline from one calendar year to the next. The improvement at age 65 might be assumed at roughly one percent per year; the improvement at age 90 at roughly half a percent per year — the magnitudes vary by age, by sex, and by which scale is in use. Applied multiplicatively to a base table, the scale projects how that table's rates will look in any future calendar year. The Society of Actuaries publishes the MP series of mortality improvement scales — MP-2014, MP-2021, and subsequent updates — each reflecting the most recent observed mortality experience and the SOA's methodology for separating signal from noise in mortality trends. Substantial uncertainty surrounds long-run mortality improvement: the trend has shown decade-scale variation, including a slowdown in the 2010s and a sharp adverse shock during the COVID-19 pandemic, and there is genuine disagreement among actuaries and demographers about whether historical improvement rates will persist, accelerate (potentially driven by biomedical advances), or decelerate (potentially driven by chronic disease, obesity, drug overdose mortality, or other adverse trends). Improvement scales are accordingly updated periodically as new experience accumulates.
In practice
For an individual planning their own lifetime income, the mortality improvement assumption matters because it determines whether the planning horizon assumed for them at age 65 reflects current conditions (no improvement assumed) or the longer expected life that contemporary SOA improvement scales project (substantial improvement assumed). A practical sense of magnitude: applying a typical MP scale extends life expectancy at 65 by roughly two to three years over a multi-decade horizon compared with using current mortality alone. A professional building lifetime income projections should be able to identify the improvement scale in use and to describe the alternative assumptions that a more conservative or more aggressive scale would produce.
In the Longevity Standard Framework
A mortality improvement scale is supporting vocabulary in the Longevity Standard framework. The framework's focal individual configuration uses a Gompertz mortality assumption with SOA credibility scaling, which is a structural approximation to a projected mortality table — the parameterization implicitly reflects a long-run mortality assumption rather than applying an MP scale to a base table directly. Where alternative mortality improvement assumptions are material to a specific finding, the framework's pattern is to name the configuration explicitly; cross-arrangement comparisons within the framework hold the mortality assumption constant so that differences in cost of income and realized value reflect arrangement structure rather than mortality basis.
Related terms
- Mortality table
- Projected mortality table
- Mortality improvement
- Cohort life table
- SOA mortality research
- Life expectancy
- Survival curve
- Cohort effect