A technical correction, India is the 5th largest economy measured by GDP as of now. IIRC US, China, Japan and Germany are ahead. Whilst India will overtake the latter 2 soon and become 3rd largest in a matter of time, it will likely stagnate at that position for a long time since China and US are way ahead.
Edit : As OP pointed out correctly, India overtook Japan last day, so it's indeed 4 th largest.
Ooh, my bad. Indeed it did overtake it. Reminds me of the UK overtake where it was a close race for some time (first India went ahead, then UK again raced ahead before India fleecing ahead finally for good).