Aims: To examine age-group and birth-cohort trends in perceived work ability in Finland in 2000-2020 and make projections of perceived work ability up to 2040 based on the observed birth-cohort development. Methods: Ten population-representative cross-sectional surveys conducted in Finland between 2000 and 2020 were used (overall N = 61,087, range 817-18,956). Self-reported estimates of current work ability in relation to the person's lifetime best on a scale from zero to ten (0-10) were classified into three groups: limited (0-5), intermediate (6-7), and good (8-10). Multiple imputation was used in projecting work ability. Results: Examining past trends by 5-year birth-cohorts born between 1961 and 1995 showed that work ability has declined steadily over time among older birth-cohorts, while in the two younger cohorts a stable development before 2017 and a steep decline between 2017 and 2020 was seen. Trends by 5-year age groups showed a declining trend of good work ability among 20-44-year-olds, a stable trend among 45-54-year-olds, and an improving trend among 55-year-olds and older was observed for the period 2000-2020. Among the under 55-year-olds the prevalence of good work ability ended up around 75% and at 68% among the 55-59-year-olds, 58% among the 60-69-year-olds and 49% among the 70-74-year-olds in 2020. Birth-cohort projections suggested a declining work ability in the future among all age groups included (30-74 years). By 2040, the prevalence of good work ability is projected to decline by 10 to 15 percentage points among 45-74-year-olds. Conclusions: The projections suggest declining work ability in the future. Efforts to counteract the decline in work ability are needed.