Clients
Westfield Capital Management serves 9,391 clients, 8,398 of them other individuals. The average client has about $3.2 million with the firm, and high-net-worth clients hold 4% of its $29.8 billion in assets.
- Individuals8,398 clients2%
- High-net-worth individuals512 clients4%
- Investment companies15 clients34%
- Pooled investment vehicles15 clients15%
- Pension and profit-sharing plans177 clients21%
- OtherCharitable organizations, State or municipal government entities, Other investment advisers, Corporations and other businesses23%
Show client breakdownHide client breakdown
| Client type | Clients | Regulatory AUM | Share | Avg. per client |
|---|---|---|---|---|
| Individuals (other than HNW) | 8,398 | $698,778,053 | 2.3% | $83K |
| High-net-worth individuals | 512 | $1,339,364,964 | 4.5% | $2.62M |
| Investment companies | 15 | $9,996,040,566 | 33.5% | $666.4M |
| Pooled investment vehicles | 15 | $4,517,391,455 | 15.2% | $301.2M |
| Pension and profit-sharing plans | 177 | $6,368,871,411 | 21.4% | $36.0M |
| Charitable organizations | 138 | $1,437,967,336 | 4.8% | $10.4M |
| State or municipal government entities | 38 | $4,292,131,725 | 14.4% | $113.0M |
| Other investment advisers | 1 | $661,015,631 | 2.2% | $661.0M |
| Corporations and other businesses | 97 | $496,421,214 | 1.7% | $5.12M |
| Total | 9,391 | $29,807,982,355 | 100% | $3.17M |
- Clients
- 8,398
- Regulatory AUM
- $698,778,053
- Share
- 2.3%
- Avg. per client
- $83K
- Clients
- 512
- Regulatory AUM
- $1,339,364,964
- Share
- 4.5%
- Avg. per client
- $2.62M
- Clients
- 15
- Regulatory AUM
- $9,996,040,566
- Share
- 33.5%
- Avg. per client
- $666.4M
- Clients
- 15
- Regulatory AUM
- $4,517,391,455
- Share
- 15.2%
- Avg. per client
- $301.2M
- Clients
- 177
- Regulatory AUM
- $6,368,871,411
- Share
- 21.4%
- Avg. per client
- $36.0M
- Clients
- 138
- Regulatory AUM
- $1,437,967,336
- Share
- 4.8%
- Avg. per client
- $10.4M
- Clients
- 38
- Regulatory AUM
- $4,292,131,725
- Share
- 14.4%
- Avg. per client
- $113.0M
- Clients
- 1
- Regulatory AUM
- $661,015,631
- Share
- 2.2%
- Avg. per client
- $661.0M
- Clients
- 97
- Regulatory AUM
- $496,421,214
- Share
- 1.7%
- Avg. per client
- $5.12M
Total
- Clients
- 9,391
- Regulatory AUM
- $29,807,982,355
- Share
- 100%
- Avg. per client
- $3.17M
What it does
Westfield Capital Management provides portfolio management for individuals and small businesses, portfolio management for investment companies, portfolio management for pooled vehicles and portfolio management for institutions. It is paid through a percentage of assets and performance-based fees.
Westfield Capital Management advises 2 private funds.
100.0% of assets ($29.81B across 9,391 accounts) are managed with discretion. $1.63B sits in a wrap fee program the firm both sponsors and manages. 7% of clients are outside the U.S., and 11 clients received advice without assets under management last fiscal year.
What the accounts hold
- Stocks98%
- Cash2%
Custodians
Westfield Capital Management’s client accounts are held mainly at The Northern Trust, with 13% of managed assets, and State Street Bank and Trust, with 9%. Westfield Capital Management has custody of $71.3M for 2 clients.
- The Bank of New York MellonThe Bank of New York Mellon · New York, NY · $2.65B9%
- The Northern TrustThe Northern Trust Company · Chicago, IL · $3.74B13%
- State Street Bank and TrustState Street Bank and Trust Co. · Boston, MA · $2.67B9%
- All other custodians$20.76B70%
Ownership and leadership
WMS Management LLC owns 75% or more of Westfield Capital Management, and William Muggia is its CEO.
- Owns 75% or more of Westfield Capital Management Company, L.P.
WMS Management LLC
Control person · since June 2008
- Owns 50% to 75% of WMS Management LLC
William Muggia
Control person · since June 2008
Robert Flores
Member of management committee · Control person · since January 2013
Richard Lee
Member of management committee · Control person · since January 2013
John Montgomery
Member of management committee · Control person · since January 2013
Kathryn Kearney
Member of management committee · Control person · since January 2021
Jenny Muller
Member of management committee · Control person · since January 2021
Matthew Renna
Member of management committee · Control person · since January 2021
Justin Moscardelli
Member of management committee · Control person · since January 2024
- Owns 10% to 25% of Westfield Capital Management Company, L.P.
MG Am Holding, Inc.
since April 2025
Monex Group, Inc.
Shareholder of mg am holding, inc. · since April 2025
Leadership
- William MuggiaChief Executive Officer and Chief Investment Officer
- Kathryn KearneyPartner, Chief Financial Officer and Chief Compliance Officer
- John MontgomeryChief Operating Officer
- Richard LeeChief Investment Officer
Staff
- 63 employees
- 19 in advisory functions
- 1 state-registered rep
Reported holdings
Westfield Capital Management’s reported 13F holdings total $30.61B across 278 positions, and the ten largest make up 29.2% of it.
- $30.61B
- Reported 13F value
- 278
- Positions
- 29.2%
- In the 10 largest
- +28.4%
- Value vs. prior quarter
- Nvidia Corporation5.3%
- Alphabet Inc. · Cap Stk CL A4.4%
- Ascendis Pharma A/s4.2%
- Axon Enterprise Inc.2.7%
- Ftai Aviation Ltd2.6%
- Apple Inc.2.4%
- Comfort Sys USA Inc.2.3%
- Broadcom Inc.1.9%
- Microsoft Corp.1.7%
- Howmet Aerospace Inc.1.7%
Together, the ten largest are 29.2% of reported value.
A 13F covers only exchange-traded long positions the firm holds with discretion, so this $30.61B is not its $29.81B in regulatory assets and does not represent any individual client's portfolio.
Fees
Westfield Capital Management is paid through a percentage of assets under management and performance-based fees.
Westfield Capital Management’s fee rates are not included in this profile. Find its brochure on the SEC’s site.
Offices and registrations
Besides its headquarters, Westfield Capital Management has 0 offices, with 1 listed address in 1 state.
Massachusetts · 1 listed address
- One Financial Center, BostonHQ
Registration details
- Legal name
- Westfield Capital Management Company, L.P.
- Headquarters
- One Financial Center, Boston, MA 02111
- Phone
- 617-428-7100
- Website
- www.westfieldcapital.com
- SEC file
- 801-69413
- Structure
- Delaware limited partnership
- Fiscal year end
- December
This directory does not report disciplinary history, for any firm or individual, in either direction. The SEC publishes the complete record, including any disciplinary events, and it is the authoritative place to check one. See this firm's record on adviserinfo.sec.gov
Common questions
How many clients does Westfield Capital Management have?
Westfield Capital Management has 9,391 clients and manages $29.8 billion for them, as of July 2026. They include 8,398 other individuals, 512 high-net-worth individuals and 177 pension and profit-sharing plans.
Source: Form ADV Part 1A, Items 5.D and 5.F, filed 1 July 2026
What services does Westfield Capital Management offer?
Westfield Capital Management provides portfolio management for individuals and small businesses, portfolio management for investment companies, portfolio management for pooled vehicles and portfolio management for institutions.
Source: Form ADV Part 1A, Item 5.G, from the SEC's 2 October 2026 data file
Which custodians does Westfield Capital Management use?
Westfield Capital Management’s separately managed account assets are held at The Northern Trust Company (Chicago, IL), with $3,737,947,986, State Street Bank and Trust Co. (Boston, MA), with $2,669,171,423 and The Bank of New York Mellon (New York, NY), with $2,645,846,256. Only custodians holding at least a tenth of those assets are named.
Source: Form ADV Part 1A, Schedule D, Section 5.K.(3), filed 1 July 2026
How many financial advisors does Westfield Capital Management have?
Westfield Capital Management has 1 investment adviser representatives registered with state securities authorities, out of 63 employees, and 19 perform investment advisory functions. None are registered representatives of a broker-dealer or licensed insurance agents.
Source: Form ADV Part 1A, Items 5.A and 5.B, from the SEC's 2 October 2026 data file
What does Westfield Capital Management invest in?
At the end of its last fiscal year, Westfield Capital Management’s separately managed accounts held 98% exchange-traded equities and 2% cash and equivalents. It advises 2 private funds.
Source: Form ADV Part 1A, Items 5.K.(1) and 7.B, from the SEC's 2 October 2026 data file
Who owns Westfield Capital Management?
Westfield Capital Management is owned through holding companies by William Muggia. Its direct owners are WMS Management LLC (75% or more) and MG Am Holding, Inc. (10% to 25%).
Source: Form ADV Part 1A, Schedules A and B, filed 1 July 2026
How does Westfield Capital Management get paid?
Westfield Capital Management is paid through a percentage of assets under management and performance-based fees. Its Form ADV lists no commissions among how it is paid.
Source: Form ADV Part 1A, Item 5.E, from the SEC's 2 October 2026 data file