A new study has ranked the five best cities to retire in on only $30,000 per year - and none of them are in the US.

Planning for retirement has long been known as a complicated and frustrating endeavor fraught with uncertainty, especially given that the average monthly social security check is only $1,404.

According to the Social Security Administration, more than 40 percent of single adults receive more than 90 percent of their income from that monthly social security check.

A study by International Living has identified the five best places in the world where that check will go far enough to live comfortably.

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A study by International Living identified Mafra, Portugal, pictured, as the best place in the world for retirees. The average cost of living in the city is $1,017 per person per month

1. Mafra, Portugal 

At the top of International Living's list is Mafra, located only 21 miles northwest of Portugal's capital.

The average cost of living in Mafra is $2,034 per couple, or $1,017 per person. 

According to the site: 'The town is a low-key place of white-washed houses trimmed in yellow and blue, lining narrow cobbled streets. 

'The scent of grilling sardines is ever-present in the air, along with the sound of laughter and clinking glasses in the village's many cafés and bars.' 

Mafra has one of the country's largest palaces, the Palace of Mafra.

It's also located only 15 minutes from Ericeira Beach, which is world-renowned for its surfing.