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Westfield Capital Management Company, L.P.
William A. Muggia · Asset Manager · Growth
Westfield Capital Management Company, L.P. is a Boston-based, employee-owned investment advisor that specializes in domestic growth equity. Founded in 1989, the firm provides actively managed investment services to a diverse client base, including institutional investors and high-net-worth individuals. Westfield utilizes a disciplined, team-oriented, and research-led approach to investing across the entire market capitalization spectrum, from small-cap to large-cap growth portfolios. Their objective is to generate consistent outperformance by identifying high-quality companies with underappreciated earnings growth and durable competitive advantages. The firm manages approximately $24 billion in assets and maintains a fundamental, bottom-up investment philosophy centered on the core belief that stock prices ultimately follow earnings trends over time.
Simulated Performance
| Metric | Value |
|---|---|
| Total return | +27.7% |
| YTD return | +20.2% |
| Sharpe ratio | 3.64 |
| Win rate | 54% |
| AUM | $12.0B |
| Inception | Oct 1, 2025 |
| Updated | Sep 18, 2026 |
Institution Status
| Field | Value |
|---|---|
| AUM | $12.0B |
| Turnover | Low (<15%) |
| Avg holding | 18 Months |
| Inception | Oct 1, 2025 |
| Website | https://www.westfieldcapital.com |
Current Holdings
Updated on Sep 18, 2026.
| Ticker | Name | Portfolio % | Return |
|---|---|---|---|
| NVDA | NVIDIA Corporation | 14.7% | +12.1% |
| GOOGL | Alphabet Inc Class A | 10.5% | +21.1% |
| ASND | Ascendis Pharma AS | 10.4% | -5.1% |
| AAPL | Apple Inc | 6.8% | +26.4% |
| AXON | Axon Enterprise Inc. | 6.0% | -23.4% |
| MSFT | Microsoft Corporation | 5.8% | -1.7% |
| SNOW | Snowflake Inc. | 4.8% | +1.0% |
| FIX | Comfort Systems USA Inc | 4.7% | +73.4% |
| AVGO | Broadcom Inc | 4.7% | -1.3% |
| FTAI | Fortress Transp & Infra Inv | 4.4% | -1.8% |
| LLY | Eli Lilly and Company | 3.9% | +21.1% |
| HWM | Howmet Aerospace Inc | 3.7% | +6.5% |
| META | Meta Platforms Inc. | 3.7% | -2.8% |
| NOW | ServiceNow Inc | 2.6% | +8.4% |
| V | Visa Inc. Class A | 2.3% | +0.8% |
| LPLA | LPL Financial Holdings Inc | 2.3% | +3.2% |
| NET | Cloudflare Inc | 2.2% | +5.6% |
| VRT | Vertiv Holdings Co | 2.2% | +41.3% |
| GH | Guardant Health Inc | 2.2% | +11.1% |
| ANET | Arista Networks | 2.1% | +2.1% |
Recent activity
| Date | Action | Ticker | Weight |
|---|---|---|---|
| Sep 14, 2026 | BUY | FIX | 4.4% → 4.7% |
| Sep 14, 2026 | BUY | NVDA | 14.4% → 14.7% |
| Sep 14, 2026 | BUY | ASND | 9.6% → 10.4% |
| Sep 14, 2026 | SELL | NOW | 2.7% → 2.6% |
| Sep 14, 2026 | BUY | FTAI | 4.6% → 4.4% |
Investment Style Analysis
Westfield Capital Management Company, L.P. is widely recognized for employing a Growth strategy. As of Sep 18, 2026, the firm oversees approximately $12.0B in assets under management (AUM). The portfolio demonstrates a clear preference for the Semiconductors and Internet Content & Information sectors, reflecting a high-conviction approach to capital allocation.
Recent Market Moves
During the latest rebalancing period ending Sep 14, Westfield Capital Management Company, L.P. made a significant move by increasing exposure to FIX. This adjustment aligns with the fund's dynamic approach to risk management and capital deployment in current market conditions.
Investment Philosophy
Westfield Capital Management employs a Growth at a Reasonable Price (GARP) investment philosophy, predicated on the conviction that stock prices are primarily driven by earnings growth over the long term. The firm’s strategy is rooted in fundamental, bottom-up research designed to identify high-quality companies with underappreciated earnings potential and sustainable competitive advantages. Investment decisions are made through a collaborative, committee-based process that integrates rigorous internal analysis with direct management engagement, including on-site visits. By maintaining a high-conviction approach and a disciplined valuation framework, Westfield aims to exploit market inefficiencies and deliver superior risk-adjusted returns across various market cycles.
Disclaimer
The content provided on this page, including the simulated portfolio performance, holdings analysis, and AI-generated insights, is for informational and educational purposes only. It does not constitute financial advice, investment recommendations, or an offer to buy or sell any securities. All data is derived from historical SEC 13F filings and other public disclosures, which have a reporting lag. The "Simulated Performance" is a hypothetical reconstruction based on past disclosures and does not represent the actual returns of the institution. Past performance is not indicative of future results. Tritonix.ai is not affiliated with Westfield Capital Management Company, L.P..
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Frequently asked questions
How is the simulated portfolio for Westfield Capital Management Company, L.P. constructed?
This simulation is powered by Tritonix AI using official SEC filings. We focus on the "Best Ideas" by filtering for only the Top 20 largest holdings and rebalancing them to 100%. The simulation tracks performance starting from Oct 1, 2025. Our AI monitors for updates every Monday to capture major shifts. This concentrated approach highlights the manager's true stock-picking skill and mirrors their actual investment returns.
What is Westfield Capital Management Company, L.P.'s largest holding?
As of the latest filing, Westfield Capital Management Company, L.P.'s top position is NVIDIA Corporation (NVDA), representing 14.7% of the portfolio. This reflects a high-conviction bet by the institution.
What is Westfield Capital Management Company, L.P.'s historical performance and risk profile?
Our simulation indicates a total return of +27.7% with a win rate of 54%. Notably, the portfolio maintains a Sharpe Ratio of 3.64, suggesting an exceptional level of risk-adjusted returns compared to the broader market.
What sectors does Westfield Capital Management Company, L.P. primarily invest in?
Westfield Capital Management Company, L.P. has a strong preference for the Semiconductors sector, which makes up 19.4% of their disclosed assets. The portfolio also has exposure to Internet Content & Information, indicating a specific thematic focus.
Is Westfield Capital Management Company, L.P.'s portfolio concentrated or diversified?
Westfield Capital Management Company, L.P. runs a moderately concentrated portfolio with 20 disclosed positions. The top 3 holdings alone account for 35.5% of the total portfolio weight, suggesting a strategy that favors broader market exposure.
How has Westfield Capital Management Company, L.P. performed in 2026?
Our AI-simulated model portfolio for Westfield Capital Management Company, L.P. tracks a Year-to-Date (YTD) return of +20.2%. This metric helps investors gauge the institution's effectiveness in the current market environment.
Does William A. Muggia manage Westfield Capital Management Company, L.P. directly?
Yes, William A. Muggia serves as the key portfolio manager for Westfield Capital Management Company, L.P., overseeing the investment strategy and final capital allocation decisions.