TOKYO -- The Bank of Japan likely set aside funds for the first time to prepare for losses on its huge holdings of Japanese government bonds should the central bank end its monetary easing policy in the future.

The bank is thought to have reserved about 450 billion yen ($4.07 billion) for the year ended in March. The amount will become known when the BOJ releases financial statements as early as next week.

The BOJ created a framework last fiscal year that permits it to set aside part of the interest income from its JGB holdings, which have ballooned through the bank's massive monetary easing program. Interest income likely grew about 30% from the prior year to around 1.3 trillion yen in fiscal 2015.

Though BOJ Gov. Haruhiko Kuroda has indicated that the bank could expand easing if it faces difficulty achieving its inflation target, the creation of the reserves is a move to prepare for an exit from monetary easing.

The central bank's JGB holdings totaled 349 trillion yen as of March 31, up about 180% in three years. Long-term interest rates, currently in negative territory, will rise and bond prices will fall should the BOJ end its monetary easing once it is sure that Japan is finally breaking free of deflation. The bank estimates that a 1 percentage-point rise in long-term rates lowers the value of its JGB holdings by 21 trillion yen.

The BOJ pays most of its net income to the government, and this payment will decline if the bank sets aside reserves. Furthermore, the central bank's profits have suffered from the lower value of foreign-currency assets due to a stronger yen. As a result, payments to the government are estimated at 400 billion yen for fiscal 2015, down sharply from 756.7 billion yen in the prior year.

Fiscal 2010 was the last time the BOJ paid less than 500 billion yen to the government. "The reserves are meant to even out swings in profit so payments to the government will not change over the long term," a BOJ official said.

But from a short-term perspective, the lower payment to the government means that taxpayers will shoulder a heavier burden. So while the BOJ's monetary easing may be propping up the economy and consumer prices, taxpayers essentially are picking up the tab.