A new detailed microsimulation, using a database of 40 million people, has examined the future of Japan’s aging population up to 2043. It projects that more people will live longer, and that overall years spent living with dementia will decrease. However, the model highlighted the diversity of impacts on different segments of the population, as Japanese women with a less than high school education and aged 75 and over may be disproportionately affected by both dementia and frailty. Better understanding where health gaps like this exist can help inform public health planning, to minimize future economic costs and support those most in need.