日本央行（BOJ）自2013年4月启动非常规宽松以来，正缓慢退出「超宽松」，其货币基础（流通的纸币与硬币，加上金融机构在BOJ的当座存款）在12月年减9.8%，但美国与欧洲同期间的降幅约为20%至30%。12月货币基础平均余额为594兆日圆（3.82兆美元），下滑部分来自自2024年8月起缩减日本国债（JGB）购买，以及在2025年6月底停止一项促进金融机构放款的计划新增贷款；全年末的降幅为2007年以来最大。

与2021年底相比，BOJ的货币基础仅减少9.6%，而美国联准会（Fed）减少16.2%、欧洲央行（ECB）减少30.5%，显示BOJ紧缩步伐相对迟缓。差异反映注入流动性的工具不同：ECB以对金融机构放款扩张资金，贷款到期偿还会使资金更快回落；Ayaka Nakamura指出，以放款为核心的资金供给更便于退出并使量化紧缩（QT）更容易。Fed以每月上限有系统地缩减公债与抵押贷款证券持有量，其持有未偿美国国债占比仅约10%；相较之下，BOJ持有（不含短期国库券的）政府债券市值占比约50%，若快速减码可能扰动供需并推升利率，因此不得不更谨慎。

日圆弱势仍持续，汇率已在1美元兑150日圆附近区间化；即使自2024年以来因Fed降息与BOJ升息而使日美利差收敛，日圆卖压仍强。以名目GDP对照，BOJ货币基础占比达89%，远高于Fed的17%与ECB的27%（QUICK），显示日本相对经济规模的资金供给更充裕；Shinichi Ichikawa指出，日本实质利率为负，使多余资金更易流向外币，结构上更倾向弱日圆。市场焦点在于BOJ缩表是否加速；Fed在12月为避免短期货币市场资金吃紧而暂停QT，货币基础下滑也可能停止。另一不确定性是Fed领导层更替：Donald Trump提名的Kevin Warsh以批评资产负债表扩张著称，市场推测其偏好QT，但政府同时追求降息与长端利率稳定，Warsh领导下的Fed短期被视为不太可能紧缩；若未来Fed再度缩表，Masahiro Ichikawa认为可能推高各期限利率、强化美元并弱化日圆。

The Bank of Japan (BOJ) is retreating from the ultra-easy stance launched in April 2013, but its exit is slower than in the U.S. and Europe: Japan’s monetary base (cash in circulation plus financial institutions’ current-account deposits at the BOJ) fell 9.8% year on year in December versus roughly 20% to 30% declines abroad. The average monetary base outstanding was 594 trillion yen ($3.82 trillion) in December, with the drop linked to reduced Japanese government bond (JGB) purchases since August 2024 and a halt at end-June 2025 to new lending under a program that encouraged bank lending; the year-end pace of decline was the largest since 2007.

Since end-2021, the BOJ’s monetary base is down only 9.6%, compared with 16.2% for the U.S. Federal Reserve (Fed) and 30.5% for the European Central Bank (ECB), reinforcing the view that BOJ tightening is relatively sluggish. The gap reflects tool choices: the ECB expanded liquidity heavily via lending to banks, which naturally shrinks quickly as loans are repaid; Ayaka Nakamura argues this lending-centered funding method makes quantitative tightening (QT) easier. The Fed has reduced Treasury and mortgage-backed securities holdings under monthly caps, and its share of outstanding U.S. Treasurys is only around the 10% range; by contrast, the BOJ holds about 50% of government bonds (excluding short-term bills) by market value, so rapid reductions risk disrupting supply-demand and sharply lifting rates, forcing a cautious pace.

Yen weakness persists, with the exchange rate entrenched near 150 per dollar; even as the Japan-U.S. rate gap narrowed since 2024 via Fed cuts and BOJ hikes, selling pressure remains. Relative to nominal GDP, the BOJ’s monetary base is 89%, far above the Fed’s 17% and the ECB’s 27% (QUICK), indicating a much more abundant money supply versus economic size; Shinichi Ichikawa cites negative real rates that encourage surplus funds to flow into foreign currencies, structurally biasing toward a weaker yen. Markets are watching whether BOJ balance-sheet shrinkage accelerates; the Fed suspended QT in December to avoid short-term money-market funding stress, and monetary-base declines may also pause. Leadership uncertainty adds risk: Donald Trump’s pick Kevin Warsh is known for criticizing balance-sheet expansion and is speculated to favor QT, but an administration seeking rate cuts and stable long-term yields implies tightening is unlikely soon; if the Fed later resumes balance-sheet reduction, Masahiro Ichikawa warns it could lift yields across maturities, strengthen the dollar, and weaken the yen.