RBI transferring Rs 1.76 lakh crore to the government became a political slugfest as everyone worried that the central banks had transferred the money from its reserves. But the Jalan panel put paid to the hopes of the government being able to dip into the RBI's accumulated reserves of 10 lakh crore. It gave the government no more than Rs 52,637 crore from the reserves. The real manna for the government came from RBI's 2018-19 P&L, which gave it a dividend of Rs 1.23 lakh crore. This amount is more than double the average annual dividend of the previous 5 years.We all wondered how the RBI made so much money last year. Most economists guessed this is partly because RBI purchased Rs 3 trillion of bonds in 2018-19 and even if these yielded a 7 percent return, it would have added an incremental income of over Rs 20,000 crore. But even that wasn't sufficient to explain why the dividend had more than doubled. Now the secret is out.CNBC-TV18 has learnt the spike is more because of an important accounting change from the start of this year. RBI has changed the way in which it account for gains made by selling dollars. And this accounting change has given it a gain of Rs 21,000 crore.ALSO READ: RBI dividend in, government tempers stimulus hopeEarlier, RBI used to mark its forex reserves to market every week. Profit on any dollar sale was the difference between sale price and previous week’s marked-to-market price. Now, the central bank has moved to pricing purchase cost of US dollar at a weighted average historical cost. The change in computation method was recommended by a committee headed by YH Malegam, board member of RBI, six years ago. It has now been accepted after being vetted by the Jalan panel.For understanding purposes, in the previous calculation method, if RBI sold dollars at Rs 71, the market to market price would be around Rs 70. Thus the gain would be approximately one rupee per dollar. Now, as the calculation is based on weighted historical cost, the value of the sold dollar can be say Rs. 55. This is because the central bank has bought dollars at different times and thus at different rates. Therefore, by using this method, each dollar sale will mean a gain of Rs 71 – Rs 55 = Rs 16. It is this gain which has resulted in an overall gain of Rs 21,000 crores.ALSO READ: RBI capital reserve: Is Rs 52,000 crore worth so much fuss?It is likely that this forex gain will be lesser in the coming years as the first calculation using the Malegam formula covered a wider timeframe. However, the change in the calculation methodology does translate to a one-time big gain for the current Narendra Modi government.