People living alone will make up nearly 40 percent of all households in Japan by 2040, a national research institute predicted Friday as more people delay or shun marriage amid a rise in divorces.

The National Institute of Population and Social Security Research also projected that households headed by people 65 or older will account for 44.2 percent that year, up from 36 percent in 2015.

The share of single-person households, already the largest at 34.5 percent as of 2015, is expected to grow further to 39.3 percent by 2040. Meanwhile, households with married couples and children, which used to account for over 40 percent of the total, are projected to slip to 23.3 percent from 26.9 percent.

As the projections cast a light on the graying population, Japan needs to develop an improved social security structure to support seniors living on their own, social security experts said.

The institute said Japan had 53.33 million households as of 2015, a level expected to peak at 54.19 million in 2023 before dropping to 50.76 million by 2040.

The number of single-person households, 18.42 million as of 2015, is forecast to peak at 20.25 million in 2030 and fall to 19.94 million by 2040.

As the overall population is predicted to decline as well, the ratio of single-person households is projected to rise to 39.3 percent, up about 5 points from 34.5 percent as of 2015, the institute said.