WESTFIELD CAPITAL MANAGEMENT CO LP MASI — MASIMO CORP............ COM

Ownership history in WESTFIELD CAPITAL MANAGEMENT CO LP  ·  66 quarters on record

AI Ownership Summary

WESTFIELD CAPITAL MANAGEMENT CO LP reported MASIMO CORP............ COM (MASI) in 66 quarterly 13F filings from 2023 Q4 through 2025 Q4. Peak portfolio weight reached 0.88% in 2025 Q3. The latest visible filing shows MASI at 0.82% of the fund.

This page tracks quarterly shares, estimated market value, portfolio weight, filing dates, and disclosure-aligned stock prices directly from SEC EDGAR 13F filings. Older history is available after unlock; the visible window still shows the most recent pattern.

What this MASI ownership page tells you

This page is designed to answer the real investor question behind a 13F filing: how meaningful was WESTFIELD CAPITAL MANAGEMENT CO LP's position in MASIMO CORP............ COM, and how did that conviction change over time? You can read the holding window, peak weight, latest reported size, disclosure timing, and quarter-by-quarter changes without piecing the story together from raw SEC rows.

Freshest filing
Latest Reported Filing
2025 Q4

MASI was reported at 0.82% of portfolio in the most recent visible filing.

High-water mark
Peak Conviction
0.88% in 2025 Q3

Peak weight helps separate a token disclosure from a real conviction holding the fund genuinely cared about.

Time in book
Holding Window
2023 Q4 to 2025 Q4

Longer holding windows often tell a very different story from short-lived tactical trades or one-quarter experiments.

Decision context
Why It Matters
Position size beats headlines

Knowing that a fund owned a stock is useful. Knowing whether it was a 0.20% placeholder or a true high-conviction position is where the signal actually starts.

MASI stock page WESTFIELD CAPITAL MANAGEMENT CO LP fund profile WESTFIELD CAPITAL MANAGEMENT CO LP full holdings
How WESTFIELD CAPITAL MANAGEMENT CO LP held MASI — position size vs. price
% of Fund (quarterly)    MASI price (quarter-end, indexed to 100)    SPY (indexed to 100)    QQQ (indexed to 100)
📋 Quarterly Holdings History 9 quarters  ▾
Quarter Action Sold % After 3M Timing Shares Change Chg % % of Fund Mkt Value Filed Price (Filed)
2025 Q4 ADDED — — — 1,522,049 +102,799 +7.2% 0.82% $198.0M 2026-02-14 (Est.) $130.15
2025 Q3 ADDED — — — 1,419,250 +238,047 +20.2% 0.88% $209.4M 2025-11-12 $149.79
2025 Q2 ADDED — — — 1,181,203 +509,724 +75.9% 0.83% $198.7M 2025-08-12 $150.13
2025 Q1 REDUCED 12.7% +1.0% ❌ 671,479 -97,379 -12.7% 0.54% $111.9M 2025-05-09 $156.57
2024 Q4 REDUCED 44.8% +0.8% ❌ 768,858 -625,198 -44.8% 0.55% $127.1M 2025-02-11 $176.90
2024 Q3 ADDED — — — 1,394,056 +262,370 +23.2% 0.84% $185.9M 2024-11-12 $160.85
2024 Q2 ADDED — — — 1,131,686 +445,586 +64.9% 0.70% $142.5M 2024-08-14 $123.93
2024 Q1 REDUCED 16.2% -20.7% ✅ 686,100 -132,376 -16.2% 0.53% $100.8M 2024-05-10 $121.76
2023 Q4 ADDED — — — 818,476 +214,795 +35.6% 0.56% $95.9M 2024-02-09 $135.07
57 older quarters hidden  —  Sign in free or upgrade to Premium to see full history

🏢 Other funds also holding MASI

As of 2026 Q1 — sorted by position size

CIBRA Capital Ltd 7.76% LOCKERMAN FINANCIAL GROUP, INC. 3Y 3.36% ALPINE ASSOCIATES MANAGEMENT INC. 3Y 7Y 1.98% Westmount Partners, LLC 1.06% Capricorn Fund Managers Ltd 3Y 0.63% Cardinal Capital Management 3Y 7Y 0.51% Ground Swell Capital, LLC 3Y 7Y 0.46% CREDIT INDUSTRIEL ET COMMERCIAL 0.32% B.O.S.S. Retirement Advisors, LLC 3Y 0.29% Andina Capital Management, LLC 0.22%

FAQ About WESTFIELD CAPITAL MANAGEMENT CO LP and MASI

These are the practical questions this page is built to answer before you even open the full history table.

How long has WESTFIELD CAPITAL MANAGEMENT CO LP reported owning MASI?

WESTFIELD CAPITAL MANAGEMENT CO LP reported MASI across 9 quarterly 13F filings, from 2023 Q4 through 2025 Q4.

What was the largest reported MASI position in WESTFIELD CAPITAL MANAGEMENT CO LP's portfolio?

The largest reported portfolio weight for MASI was 0.88% in 2025 Q3.

What is the latest reported MASI position on this page?

The most recent filing on this page is 2025 Q4, when WESTFIELD CAPITAL MANAGEMENT CO LP reported 1,522,049 shares, equal to 0.82% of portfolio, with an estimated market value of $198.0M.

What does the chart on this MASI ownership page compare?

The chart compares WESTFIELD CAPITAL MANAGEMENT CO LP's quarterly MASI portfolio weight with the stock's indexed share price, so you can see whether the fund was building, trimming, or holding the position as price moved.

How well did WESTFIELD CAPITAL MANAGEMENT CO LP time their MASI position?

Based on 13F filing dates vs. subsequent MASI price moves, WESTFIELD CAPITAL MANAGEMENT CO LP correctly timed 33 out of 65 reported position changes (51%). The annualised alpha on MASI relative to SPY over the holding period was +3.7%.

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