Thai civil servant Supapan Pullbangyung spends just under half of her salary on caring for her 75-year-old father, who suffers from diabetes and dementia.

Hers is one of many Thai families looking after elderly relatives at a cost that countrywide adds up to just under a third of household income.

The number of families facing similar problems will balloon as the population ages at a rate among the fastest in Southeast Asia.

Thailand's working-age population is expected to shrink by 11 percent by 2040.

The rising cost of care is an additional burden to households struggling with record debt that is a drag on consumption and stunting the economy.

"I struggled for months and it took a while to adjust," says Supapan, who lives in Nonthaburi province, just north of the capital, Bangkok.

Looking after her father costs at least 15,000 baht ($430) a month, she says, a little less than half what she earns.

A culture of filial piety in which families feel obliged to care for their elderly means more often than not they absorb the expense of looking after parents and grandparents.

A poor savings culture has left many people ill-prepared to help themselves financially in old age, meaning they must rely on working family members.

More than a quarter of the 66 million population has not saved for old age, according to a 2014 survey, one of many factors contributing to the government considering raising the age of retirement from 60 and urging businesses to hire more older people.

"It is going to be a burden on the younger generation," says Sutayut Osornprasop, a human development specialist at the World Bank.

Households caring for elderly relatives spend at least 7,620 baht on them per month, according to the Health Insurance System Research Office, a state agency under the Ministry of Public Health.

That's more than 28 percent of the average 2015 monthly household income of 26,915 baht.

Kangsadan Sagulpongmalee, 40, is a lecturer in Petchaburi province who is caring for her 70-year-old diabetic father. He underwent spinal surgery in December and is recovering at Wellness City, a privately run complex for the elderly near the city of Ayutthaya, north of Bangkok.

"My salary earned as a lecturer isn't enough at all. I have to spend my parents' life savings," she says.

Kangsadan plans to move her father to a house near her workplace once he has recovered so she can look after him.

"It'll be very expensive, but I'll try my best to handle everything."

A lower cost of living in Thailand's rural areas means some who had moved to the city for work are considering going back to care for parents.

Noppasorn Suebsai, 21, is one of them.

"If you live in the countryside where we don't spend as much the cost will be less," says Noppasorn, a Bangkok-based nursing student. "I don't think I will struggle as much to care for my parents."