TOPIX vs Nikkei 225 - Composition, Methodology, and Index Behavior
Reading time: about 3 min
TOPIX and the Nikkei 225 are Japan's two flagship equity indices. The choice of methodology - market-cap weighting versus price weighting - shapes very different return profiles and constituent biases.
Two Indices, Two Designs
TOPIX (Tokyo Stock Price Index) is a market-cap-weighted index calculated by the Tokyo Stock Exchange, in principle covering all TSE Prime constituents (around 1,650 companies as of 2026), with a base of 100 on January 4, 1968. The Nikkei 225 is a price-weighted index calculated by Nihon Keizai Shimbun, comprising 225 companies selected from TSE Prime, with a starting value of 176.21 yen on May 16, 1949 and Dow-style divisor adjustments to maintain continuity. Both seek to measure the Japanese equity market, but their fundamentally different methodologies produce different returns and different constituent biases.
Effect of Market-Cap vs Price Weighting
Market-cap weighting in TOPIX gives heavy weight to large companies such as Toyota, Mitsubishi UFJ, and Keyence, which drive most of the index's movement. The Nikkei 225, in contrast, applies a simple price average (with divisor adjustments), so high-priced stocks dominate. Fast Retailing (Uniqlo) has a market cap of around 14 trillion yen but a high share price, which can give it more than a 10% weight in the Nikkei 225. Toyota, despite being one of Japan's largest by market cap, sits at a few percent in the Nikkei 225 because of its mid-range share price. Days when Fast Retailing moves sharply often see the Nikkei 225 diverge meaningfully from TOPIX.
Sector Composition
The Nikkei 225 is selected with sector balance in mind, blending growth and traditional sectors across 225 names. TOPIX, being market-cap-weighted, automatically tilts toward sectors with the largest aggregate market value (financials, autos, technology). As of 2024, information technology accounts for around 50% of the Nikkei 225 (including Fast Retailing in the index's GICS classification), creating concentration risk. TOPIX is more diversified, with financials at around 12%, consumer goods around 20%, and IT around 22%. Investors should note that buying a Nikkei 225 ETF effectively concentrates exposure into Fast Retailing and SoftBank Group.
Historical Divergence
Although both indices track Japanese equities, their annual returns can diverge meaningfully. In 2023, TOPIX returned about +25% and the Nikkei 225 +28% - close to parity. In other years the gap has been 5-10 percentage points. During the 1989 bubble peak, the Nikkei 225 reached its all-time high of 38,915 yen, but TOPIX peaked at 2,884 points; even when the Nikkei 225 set a new high in 2024, TOPIX had not yet returned to its bubble peak. This illustrates how single names like Fast Retailing can pull the Nikkei 225, while TOPIX more faithfully represents the market as a whole.
Price Index vs Total Return
When comparing returns, the distinction between price indices (capital gains only) and total return indices (dividends reinvested) also matters. The TOPIX and Nikkei 225 levels reported in the media are usually price indices excluding dividends; to gauge real long-term investment outcomes, the dividend-inclusive total-return versions should be referenced. Both indices have total-return versions, and TOPIX - with its larger weighting in high-dividend financial and materials sectors - tends to show a wider dividend-inclusive gap than the price index suggests. For individual investors who assume long-term holding and reinvestment, comparing cumulative returns including dividends, rather than price-index movements alone, is a practical basis for choosing index-tracking products. When selecting a tracking ETF, note that whether it reinvests or distributes dividends changes the compounding effect. Both indices also periodically revise constituents and free-float weights, so the index contents are not fixed; TOPIX has been phasing in changes alongside the TSE market restructuring. When holding an index long term, understanding its design philosophy - how it selects and rotates constituents - helps avoid surprise at unexpected moves.
Choosing Among Investment Products
Numerous ETFs and mutual funds track both indices. Nikkei 225 ETFs (e.g., 1321, 1330) are highly liquid and heavily traded, but constituent concentration is a real consideration. TOPIX ETFs (e.g., 1306, 1308) hold more names and provide broader diversification. Foreign investors and institutional benchmarks typically rely on TOPIX or MSCI Japan, and TOPIX is the standard reference for institutional performance comparisons. This article is for informational purposes only and does not recommend any specific index-tracking product. Investment decisions are made at your own discretion.