Abstract Introduction The prevalence of atrial fibrillation (AF) is strongly associated with age, and with increasing life expectancy worldwide, the number of AF patients has been steadily rising. However, long-term projections of AF prevalence are scarse. Purpose To predict the prevalence and the number of patients with AF in Finland from 2021 until 2070. Methods In the Finnish Anticoagulation in Atrial Fibrillation (FinACAF) study we gathered data of all AF patients from all national health care registers (hospitalizations and outpatient specialist visits, primary health care contacts, and reimbursements for prescription medicines) from 2004 to 2018. The prevalence of AF on December 31st 2018 was calculated as the number of patients alive with AF divided by the number of Finnish population. We utilized age- and sex-specific prevalences on year 2018 to predict the prevalence by sex and 5-year age groups, using a 1-year time interval of AF in Finland between years 2021 and 2070. We obtained the projection for population structure in Finland between 2021 and 2070 from Statistics Finland. The prevalences in 2070 are provided for population ≥20 years as well as for populations ≥65 years, ≥75 years, and ≥85 years. Results In 2018, a total of 226 847 patients with the diagnosis of AF were documented in Finland. The number of adult patients with AF is predicted to increase strongly up to 2040 with a slower increase from 2040 to 2060, and again a faster increase is estimated from 2060 up to our final estimation of 2070. In total, the number of AF patients will increase with 60% until the year 2070. In 2021, prevalence of AF was 5.5% in adults and prevalence rate will increase to 8.6% in 2070. Proportion of men will be from 54.7 % to 56.0%, and the prevalence will be higher in men compared to women in all age groups with the exception in the age group ≥85 years. Among the population ≥65 years the prevalence in 2070 will be 19.7 %, and in the elderly, ≥75 years, the prevalence of AF will 25.6% and in the oldest, ≥85 years, 31.7%. In 2070 73.3 % of patients with AF are over 75 years, and 38.8% are over 85 years old. Conclusions Drawing upon extensive nationwide data covering all levels of care, our estimates indicate a continual rise in the number of AF patients in Finland until the year 2070. Notably, throughout the projected period, there is a discernible increase in the proportion of older and the oldest patients, highlighting the demographic shift in AF prevalence.Patients with AF 2021-2070 in Finland