Married couples in South Korea received one of the smallest tax breaks among other advanced economies, a study showed Tuesday, although the government has been trying to promote marriage to tackle low birth rates.

The effective income tax rates for singles ranged between 0.9 and 13 percent in 2013, which was 0.2-0.6 percentage point more than those for married couples, Ahn Jong-seok, a researcher at the Korea Institute for Public Finance, said in a report.

The effective tax rate is the average rate at which an individual is taxed on earned income, which also considers government subsidies and tax returns.

The discrepancy is significantly smaller than the average for the Organization for Economic Cooperation and Development (OECD) countries, whose tax rate gap between singles and couples is up to 2.9 percentage points.

It means that married people in South Korea received smaller tax breaks for the same income than those in the 33 other mostly rich nations in 2013, the report said.

Between two-person and four-person households, the difference between South Korea and the OECD average was even greater.

While the effective income tax rate for the average family of four in South Korea came at 8.3 percent, the comparable figure for OECD nations was negative 7.5 percent as they received more subsidies than they paid in taxes.

Not only were single people in South Korea treated more or less equally as their married counterparts, they paid less taxes in absolute terms compared to their OECD peers, it noted.

The findings underline concerns that South Korea may not be giving enough incentives for people to marry even as its birth rate remains at historic lows while the aging population is growing rapidly.

The birth rate remained at the lowest record of 8.6 live births per 1,000 people for the second straight year. Even by absolute terms, South Koreans gave birth to 435,300 babies, or the second lowest number since the data were first collected in 1970, according to government data.

The number of South Koreans tying the knot also fell for the third straight year in 2014 to 305,000, data showed. (Yonhap)