Here is the Religious demography of India based on 2001 Census.

Note regarding Muslim population: The muslim population count is questionable as illegal Bangladeshi immigrants who are in crores are not counted. According to Justice K.M. Yusuf, a retired judge of the Calcutta High Court and Chairman of the West Bengal Minority Commission in an interview said the true percentage is between 20-25%. Here are the excerpts (published in The Hindu October 01, 1999 ).

(Rasheeda Bhagat: Interviewer)Would you agree with the point of view that the real percentage of the Muslim population in India is about 25 per cent?

(Justice Yusuf )There is no denial. It may be more. Anyway, it cannot be less than 20 per cent. It could be 25 per cent. I do not say like some others that it is 30 per cent. It is quite a substantial chunk.

Note regarding Christian population: The Christian population in India officially stands at 2.34% which everybody including Christians don't trust.. According to the Christian estimate collected by Joshua Project which is based on Church membership, Christians account for 6% of Indian population. Check the following link for religious demography based on Church estimates

http://www.crusadewatch.org/index.php?option=com_content&task=view&id=570&Itemid=61

Majority of Christians do not report their religion as Christianity for 2 reasons i.e., a) loss of caste based reservation benefits b)Church leaders do no want to raise alarm bells with sudden increase in numbers. Indian Christian leaders conveniently use Census data to portray minority status and pursue persecution strategy while using the church count data to show progress and request more funds from foreign donors.