Currently, the Indian economy is about $3 trillion. The economy is expected to reach $30 trillion by 2050. That is a 10-fold hike in 28 years or a $1 trillion increase every year from now on.
The following are the estimates of World Bank and OECD
The current growth rate is 8.2% but this growth rate may not be sustained as the GDP expands. The below graph from OECD shows the expected growth rate of India over the next few years and in comparison, with other countries and the world.