Japan’s monetary base decreased by 9.8% year-on-year in December. This follows a decline of 8.5% in the previous month.
The monetary base is a key measure of the money supply in an economy. It consists of currency in circulation and deposits held by financial institutions at the central bank.
Japan Monetary Base Contraction
The continued contraction of Japan’s monetary base, now at -9.8%, signals an acceleration of the Bank of Japan’s quantitative tightening. This faster-than-expected pace reinforces a hawkish policy stance. We should anticipate this putting further upward pressure on the Japanese Yen in the coming weeks.
This policy move is a direct response to persistent inflation, which we saw hovering above the 2% target for most of 2025, with November’s core CPI coming in at 2.7%. The tightening follows the two policy rate hikes enacted last year, which ended the negative interest rate era. The BoJ’s commitment to this path appears stronger than the market previously priced in.
For currency traders, this reinforces the case for long Yen positions, particularly against currencies where the central bank is poised to pause or cut rates. During 2025, we watched the USD/JPY pair fall from over 150 to around the 138 level as this policy divergence began to take hold. This trend now has fresh momentum to continue its move lower.
Impact on Equity and Currency Markets
In equity derivatives, the strengthening Yen is a significant headwind for the export-heavy Nikkei 225. We should consider buying put options or establishing bearish call spreads to hedge against or profit from potential downside in the index. The market struggled for direction in the final quarter of 2025 as this currency effect began to impact earnings forecasts.
The BoJ’s aggressive stance will likely fuel higher volatility in both currency and equity markets. This creates an opportunity to purchase volatility instruments, like straddles on the Nikkei 225. Such a strategy would be profitable if the index makes a large move in either direction as it adjusts to this accelerated tightening schedule.
