Singapore's Central Provident Fund (CPF) maintained its top position among similar retirement systems in Asia for the third consecutive year, despite slipping slightly in its overall score.

It racked up a score of 64.7 out of 100 in the Melbourne Mercer Global Pension Index - which ranked 25 countries on the adequacy, sustainability and integrity of their retirement plans - down from 65.9 last year.

The score gave it a "C+" grade, down from "B" last year. The "C+" grade is for a pension system that has "some good features, but also has major risks and/or shortcomings that should be addressed".

Other countries ranked with a "C+" grade are Germany and Ireland in the index.

Singapore's rating places it ahead of five other Asian nations ranked - China, India, Indonesia, Japan and South Korea, which were given a "D" grade. Singapore also beat developed nations such as Germany and the United States.

Singapore was ranked 10th overall, with Denmark taking top spot with a score of 81.7, earning it an "A" grade. India was last with 40.3.

The survey was carried out by consulting firm Mercer and the Australian Centre for Financial Studies, a non-profit group.

The drop in Singapore's score is attributable to a change in calculation which reduced the level of pension assets as a percentage of Singapore's economic output, a decrease in the net household savings rate here, and a continued decline in mortality rates for Singapore.

Mr Neil Narale, Mercer's Asia retirement leader said that while Singapore's retirement income system remains among the best in Asia, it is not the best globally.

"Improvement will be influenced by the legislative and regulatory environment. However, Singapore is on the right track, having announced improvements to CPF next year, including increasing the wage limit, contributions and guaranteed investment returns for older members, and introduction of the Silver Support Scheme to help low-income retirees."