Cairo's population is set to grow by 500,000 this year, more than any other city in the world, adding to the pressure on an Egyptian economy struggling to recover from six years of political turmoil.
Greater Cairo, a metropolitan area including the cities of Cairo parts of the Giza and Qalyubia, is home to some 22.8 million people and will gain another half a million in 2017, a Euromonitor International report released last week shows.
That represents a quarter of Egypt's 92 million.
The national natural population growth of 2.4% per year is double the average of other developing countries, said Mohamed Abdelgalil, adviser to official statistics agency CAPMAS.
Stinging poverty in southern Egypt leads many families to have several children in the hope they can become sources of income.
Those children eventually migrate to larger cities for job opportunities scarce in their hometowns.
Maysa Shawky, the head of the National Population Council, told Reuters that awareness campaigns at universities and schools have begun as part of a national population strategy.
Internal migration is one of the main causes of overpopulation in Cairo.
Egypt lists 351 slums as "unsafe", most of them in the sprawling capital where the poorest have built ramshackle homes that lack basic amenities such as mains sewage and water.
Some 850,000 people are believed to live in such dangerous slums.
New administrative capital
"For the average citizen to not be affected by hikes in the prices of goods and services, the economic growth rate must be double the natural population increase rate," Abdelgalil said.
Egypt's economic growth was 4.3% in 2015-2016 - not enough to achieve that.
The IMF expects it to be about 4% this year.
A new administrative capital, announced in March 2015, is intended partly to reduce the crowding in Cairo.
Some 45 km (28 miles) to the east, it will be home to government ministries, housing and an airport.
People will start moving to the as yet-unnamed new city in 2018, said Khaled Abbas, assistant to the housing minister for technical affairs.
Work on 17,000-18,000 residential units is nearing completion and they will be put up for sale in April.