Voluntary contributions and coupon sales were the key income sources for the ruling BJP and the Congress (INC) while the two parties' cumulative total income amounted to Rs 832.42 crore in the financial year 2016, according to the Association for Democratic Reforms (ADR).
In 2015-16, the BJP's income from unknown sources was Rs 460.78 crore while that of INC was Rs 186.04 crore.
Income from "unknown sources" refers to those where the source is not declared for donations below Rs 20,000. Such income includes those from the sale of coupons, relief fund, miscellaneous income, voluntary contributions and contribution from meetings or morchas, stated the report.
Among the unknown sources of funding, maximum funds were collected under "voluntary contributions" by the BJP, which amounted to Rs 459.56 crore in fiscal 2016, it said.
The total amount of voluntary contributions, including donations of over Rs 20,000, received by the BJP was Rs 536.41 crore in 2015-16.
As for the Congress, the report said the party collected Rs 167.96 crore from "sale of coupons" during the same period.
"Total income of seven national parties for 2015-16 was Rs 1,033.18 crore, of which the parties spent Rs 754.45 crore and declared an unspent amount of Rs 278.73 crore (26.98 per cent unspent of total income)," the report added.
Among the seven national parties, the report said the BJP had the highest total income at Rs 570.86 crore in 2015-16, followed by the Congress at Rs 261.56 crore, the CPM (Rs 107.48 crore), the BSP (Rs 47.39 crore), the Trinamool Congress (Rs 34.58 crore), the NCP (Rs 9.14 crore) and the CPI (Rs 2.18 crore).
According to the analysis for 2015-16, 23 per cent of BJP's total income remained unspent whereas it was 26 per cent in the case of the Congress.
Compared to its total income of Rs 970.43 crore in 2014- 15, the BJP saw the amount fall 41 per cent to Rs 570.86 crore in 2015-16.
The Congress saw total income drop 56 per cent to Rs 261.56 crore in 2015-16, from Rs 593.31 crore in the year-ago period.
The report further said the contribution statements submitted by the political parties declaring names and other details of donors who contribute above Rs 20,000 are the only known sources of income parties.
Funds from "known sources (donations above Rs 20,000)" accounted for Rs 97.27 crore of the two parties' total income in 2015-16 put together.
Of the BJP's total income, Rs 76.85 crore came from such sources whereas the same stood at Rs 20.42 crore in the case of the Congress.
Apart from known and unknown sources, the total income includes "other known income" -- which include sale of moveable and immoveable assets, old newspapers, membership fees, delegate fee, bank interest, sale of publications and levy. In 2015-16, the BJP and the Congress received Rs 33.23 crore and Rs 55.10 crore, respectively, by way of "other known income".
Income from bank interest accounted for Rs 19.617 crore and Rs 44.67 crore for the BJP and the Congress, respectively.
"The BJP declared a total income from donations above Rs 20,000 of Rs 76.85 crore, a mere 14.33 per cent of total donations, from donors whose details are available," the report said.