China has already surpassed the US as the most powerful economy in the world by purchasing power parity, but India will also overtake the US by 2050, according to a report by the professional-services giant PwC.
In a report titled “The long view: how will the global economic order change by 2050?” PwC ranked 32 countries by their projected global gross domestic product, measured by purchasing power parity.
Macroeconomists use PPP to determine the economic productivity and standards of living among countries.
As of 2016, India was in third place in PwC’s table with a PPP of $8.721 trillion, but by 2050 it is projected to grow to a huge $44.128 trillion. If you look at the following table, you can see how the growth rate of some emerging-market economies are seen to leap past some of their developed-market counterparts: 
“Emerging economies offer great opportunities for business – the numbers in our report make it clear that failure to engage with these markets means missing out on the bulk of economic growth we expect to see in the world economy between now and 2050,” said John Hawksworth, the chief economist at PwC. “To succeed, businesses will need to adopt strategies with the right mix of flexibility and patience to ride out the short-term economic and political volatility that is a normal feature of emerging markets as they mature.”
PwC predicts that another emerging-market economy, Indonesia, will move up the rankings and overtake Europe’s powerhouse economy Germany and even Russia by 2050.
The world economy will double in size by 2042, PwC forecasts, "growing at an average annual rate of just over 2.5% between 2016 and 2050."
"Growth is expected to be driven largely by emerging market and developing countries, with the E7 economies of Brazil, China, India, Indonesia, Mexico, Russia and Turkey growing at an annual average rate of 3.5% over the next 34 years, compared to an average of just 1.6% for the advanced G7 nations of the US, Canada, France, Germany, Italy, the UK and Japan," the firm added.
Hawksworth said, however: "The global economy faces a number of challenges to prosperous economic growth in the long-term. Ageing populations and climate change require forward-thinking policy which equips the workforce to continue to make societal contributions later on in life and promotes sustainable development.
"Falling global trade growth, rising inequality and increasing global uncertainties are intensifying the need to create diversified economies which offer opportunities for everyone in a broad variety of industries."