The Bank of Japan's drive to change the way inflation is measured suggests a tapering of bond-buying stimulus will come sooner than markets think.

The central bank is lobbying for a revision to housing cost estimates that could boost its preferred price gauge to within half a percentage point of its 2 percent goal, according to UBS AG. The government is conducting a once-in-five-year re-basing of consumer price indexes, due to take effect July 2016, the middle of BOJ Gov. Haruhiko Kuroda's six-month target period for reaching the CPI goal.

A measure of rents in the world's third-largest economy fell 0.3 percent in May from a year earlier, depressing core CPI to near zero.