NAMS insider ownership: who sold, why, and what they still hold

What stands out

Three insiders sold $18.5M with no disclosed plan: Michael Davidson ($14.8M), Louis Lange ($2.2M) and Johannes Kastelein ($1.6M). The filings don't state a reason.Michael Davidson: largest such sale, Mar 2, 2026 · Louis Lange: largest such sale, Mar 11, 2026 · Johannes Kastelein: largest such sale, Feb 20, 2026

Michael Davidson bought 10K shares for $226K, first on Sep 14, 2026.Purchase, Sep 14, 2026

A share of stake is shown for 0 of the 6 officers and directors who sold. 15 are left out

Left out: James Topper, Michael Davidson, Johannes Kastelein, Louis Lange, Michael Marino III, Douglas Kling, Mayur Somaiya, Juliette Audet, Louise Kooij, Adele Gulfo, Kamp van der, John Smither, William Lewis, Mark McKenna and Robert Gunning (share of stake is being verified).

Disclosed company stock is not an insider's whole wealth.

Who sold, and how much of their stake

Officers and directors, past 12 months. Their share of stake is being verified and is not shown yet; amounts and trading plans are below.

Michael Davidson

Chief Executive Officer, Director

Not confirmed

Share of stake not shown: share of stake is being verified. Why

$25.3M42% planned 58% no plan disclosed

Louise Kooij

Chief Accounting Officer

Not confirmed

Share of stake not shown: share of stake is being verified. Why

$16.8MDisclosed plan

Johannes Kastelein

Chief Scientific Officer, Director

Not confirmed

Share of stake not shown: share of stake is being verified. Why

$15.5M90% planned 10% no plan disclosed

Mayur Somaiya

Chief Financial Officer

Not confirmed

Share of stake not shown: share of stake is being verified. Why

$3.4MDisclosed plan

Louis Lange

Director

Not confirmed

Share of stake not shown: share of stake is being verified. Why

$2.2MNo plan disclosed

All 6 sellers

Selling by month

Officers and directors, Oct 2025 to Oct 2026. Each sale is counted once: under a disclosed plan, else to cover taxes, else no plan disclosed.

Disclosed planTo cover taxesNo plan disclosedOne dollar scale for every month; the tallest bar is labeled

Recent activity

Past 30 days, Sep 14, 2026 to Oct 13, 2026

Sep 30, 2026Johannes Kastelein sold 50K shares ($1.3M) under a disclosed trading plan. 50K shares came in from vesting or option exercises the same day, so the holding rose by 0 net.

Who	Shares	Price	% of total stake	Total stake after	Trade date	Filed
Johannes Kastelein Chief Scientific Officer, Director	50,246	$25.03	n/a	n/a	Sep 30, 2026	Oct 2, 2026

Sep 14, 2026Michael Davidson bought 10K shares ($227K).

Who	Shares	Price	% of total stake	Total stake after	Trade date	Filed
Michael Davidson Chief Executive Officer, Director	10,000	$22.65	n/a	n/a	Sep 14, 2026	Sep 15, 2026

"% of total stake" is the shares in an event against all the vested shares the person held that day, across every share class and holding entity, after that day's vesting. "n/a" means the person's holdings are not confirmed, or the row is a purchase. "Holdings record incomplete" means more shares were sold than the filings show the person held that day, so a percentage would be wrong.

Outside holders, reported separately

James Topper reported no open-market sales in the past 12 months. Large shareholders and the funds or companies that board members represent are not part of management, so they are left out of the figures above.

Details

Common questions

Is the NewAmsterdam Pharma Co N.V. CEO selling stock?

Yes. Michael Davidson sold 762K shares ($25.3M) in the past 12 months, 42% of it under a trading plan disclosed in the filings.

Why are NewAmsterdam Pharma Co N.V. insiders selling?

Filings rarely give a reason, and we don't guess at one. What they show is how the sales were made: 71% of sales by value ran under 10b5-1 trading plans disclosed in the filings, 0.1% were to cover taxes and 29% had no disclosed plan. A trading plan schedules sales in advance.

Are any NewAmsterdam Pharma Co N.V. insiders buying?

Yes. 1 officer or director reported 1 purchase in the past 12 months (Form 4 code P; rows the filings describe as reinvested dividends, plan purchases, private deals or moves into the person's own trust are not counted).

The evidence

Who sold6 officers and directors: amount, % of holdings, trading plan

Who sold	Amount	% of holdings	Trading plan
Michael Davidson Chief Executive Officer, Director	$25.3M 762K shares	Not confirmed share of stake is being verified. Why	42% under a disclosed plan 58% no plan disclosed
Louise Kooij Chief Accounting Officer	$16.8M 503K shares	Not confirmed share of stake is being verified. Why	Disclosed plan
Johannes Kastelein Chief Scientific Officer, Director	$15.5M 527K shares	Not confirmed share of stake is being verified. Why	90% under a disclosed plan 10% no plan disclosed
Mayur Somaiya Chief Financial Officer	$3.4M 105K shares	Not confirmed share of stake is being verified. Why	Disclosed plan
Louis Lange Director	$2.2M 73K shares	Not confirmed share of stake is being verified. Why	No plan disclosed
John Smither Director	$41K 1.6K shares	Not confirmed share of stake is being verified. Why	To cover taxes

Board members representing outside shareholders, reported separately: James Topper. Details

The full ownership picture0 of 15 officers and directors confirmed

Vested shares across all share classes, held directly and through trusts, LLCs and family members, as reported on SEC Forms 3, 4 and 5. Unvested awards and options are never counted as owned shares.

Insider

Held Oct 13, 2025

Sold

Held Oct 13, 2026

Still held

James Topper

Holdings and share of stake are being verified. Share-of-stake figures and holdings for this company are held back while they are verified. Sales and other transactions for James Topper are complete.

Director

n/a

Vesting, gifts, unvested awards and holding lines for James Topper

Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for James Topper are complete; balances and unit counts will be added when the check is finished.

0gifted (net of own trusts)

Michael Davidson

Chief Executive Officer, Director

n/a

−762K

n/a

Vesting, gifts, unvested awards and holding lines for Michael Davidson

Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for Michael Davidson are complete; balances and unit counts will be added when the check is finished.

0gifted (net of own trusts)

Stock options (not counted as shares):

Options held	Strike price	Expires	Intrinsic value (estimate)
1,021,485	$10.90	Jan 1, 2033	$14.4M
2,440,538	$10.00	Nov 22, 2032	$36.7M
239,267	n/a	Jul 6, 2031	n/a
1,039,939	$11.17	Jan 1, 2034	$14.4M
670,467	$25.85	Jan 6, 2035	$0
364,000	$35.45	Jan 7, 2036	$0

Estimate: options held × ($25.03 − strike price), using the most recent insider trade price on Form 4 (Sep 30, 2026), not a market close.

Johannes Kastelein

Chief Scientific Officer, Director

n/a

−527K

n/a

Vesting, gifts, unvested awards and holding lines for Johannes Kastelein

Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for Johannes Kastelein are complete; balances and unit counts will be added when the check is finished.

0gifted (net of own trusts)

Stock options (not counted as shares):

Options held	Strike price	Expires	Intrinsic value (estimate)
477,347	$10.90	Jan 1, 2033	$6.7M
971,726	$10.00	Nov 22, 2032	$14.6M
500,000	$11.17	Jan 1, 2034	$6.9M
200,000	$25.96	Jan 2, 2035	$0
115,000	$35.45	Jan 7, 2036	$0
1,171,902	n/a	Jul 6, 2031	n/a
520,229	n/a	Jul 6, 2031	n/a
344,983	n/a	Jul 6, 2031	n/a
970,229	n/a	Jul 6, 2031	n/a
395,229	n/a	Jul 6, 2031	n/a

Estimate: options held × ($25.03 − strike price), using the most recent insider trade price on Form 4 (Sep 30, 2026), not a market close.

Louis Lange

Director

n/a

−73K

n/a

Vesting, gifts, unvested awards and holding lines for Louis Lange

Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for Louis Lange are complete; balances and unit counts will be added when the check is finished.

0gifted (net of own trusts)

Stock options (not counted as shares):

Options held	Strike price	Expires	Intrinsic value (estimate)
57,583	$10.90	Jan 1, 2033	$814K
94,835	$10.00	Nov 22, 2032	$1.4M
84,957	$10.00	Nov 22, 2032	$1.3M
75,351	n/a	Jul 8, 2031	n/a
85,229	n/a	Jul 8, 2031	n/a
10,000	$11.17	Jan 1, 2034	$139K
32,500	$25.85	Jan 6, 2035	$0
15,300	$35.45	Jan 7, 2036	$0

Estimate: options held × ($25.03 − strike price), using the most recent insider trade price on Form 4 (Sep 30, 2026), not a market close.

Michael Marino III

Chief Legal Officer and Corporate Secretary

n/a

Vesting, gifts, unvested awards and holding lines for Michael Marino III

Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for Michael Marino III are complete; balances and unit counts will be added when the check is finished.

0gifted (net of own trusts)

Stock options (not counted as shares):

Options held	Strike price	Expires	Intrinsic value (estimate)
315,000	$18.11	Jun 1, 2035	$2.2M

Estimate: options held × ($25.03 − strike price), using the most recent insider trade price on Form 4 (Sep 30, 2026), not a market close.

Douglas Kling

Chief Operating Officer

n/a

Vesting, gifts, unvested awards and holding lines for Douglas Kling

Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for Douglas Kling are complete; balances and unit counts will be added when the check is finished.

0gifted (net of own trusts)

Stock options (not counted as shares):

Options held	Strike price	Expires	Intrinsic value (estimate)
5,996	$10.90	Jan 1, 2033	$85K
162,702	$10.90	Jan 1, 2033	$2.3M
372,829	$10.00	Nov 22, 2032	$5.6M
126,145	n/a	Jul 6, 2031	n/a
323,771	$11.17	Jan 1, 2034	$4.5M
250,000	$25.96	Jan 2, 2035	$0
47,251	n/a	Jul 6, 2031	n/a

Estimate: options held × ($25.03 − strike price), using the most recent insider trade price on Form 4 (Sep 30, 2026), not a market close.

Mayur Somaiya

Chief Financial Officer

n/a

−105K

n/a

Vesting, gifts, unvested awards and holding lines for Mayur Somaiya

Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for Mayur Somaiya are complete; balances and unit counts will be added when the check is finished.

0gifted (net of own trusts)

Stock options (not counted as shares):

Options held	Strike price	Expires	Intrinsic value (estimate)
662,814	$9.26	Nov 1, 2033	$10.5M
80,000	$11.17	Jan 1, 2034	$1.1M
220,000	$25.96	Jan 2, 2035	$0
115,000	$35.45	Jan 7, 2036	$0

Estimate: options held × ($25.03 − strike price), using the most recent insider trade price on Form 4 (Sep 30, 2026), not a market close.

Juliette Audet

Chief Strategy and Business Officer

n/a

Vesting, gifts, unvested awards and holding lines for Juliette Audet

Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for Juliette Audet are complete; balances and unit counts will be added when the check is finished.

0gifted (net of own trusts)

Stock options (not counted as shares):

Options held	Strike price	Expires	Intrinsic value (estimate)
250,000	$21.37	Apr 1, 2034	$915K
100,000	$25.96	Jan 2, 2035	$0
30,000	$20.03	May 1, 2035	$150K

Estimate: options held × ($25.03 − strike price), using the most recent insider trade price on Form 4 (Sep 30, 2026), not a market close.

Louise Kooij

Chief Accounting Officer

n/a

−503K

n/a

Vesting, gifts, unvested awards and holding lines for Louise Kooij

Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for Louise Kooij are complete; balances and unit counts will be added when the check is finished.

0gifted (net of own trusts)

Stock options (not counted as shares):

Options held	Strike price	Expires	Intrinsic value (estimate)
10,000	$11.90	May 18, 2033	$131K
43,134	$10.90	Jan 1, 2033	$609K
80,015	$10.00	Nov 22, 2032	$1.2M
70,494	$11.17	Jan 1, 2034	$977K
80,000	$25.96	Jan 2, 2035	$0
53,500	$35.45	Jan 7, 2036	$0
213,073	n/a	Jul 6, 2031	n/a

Estimate: options held × ($25.03 − strike price), using the most recent insider trade price on Form 4 (Sep 30, 2026), not a market close.

Adele Gulfo

Director

n/a

Vesting, gifts, unvested awards and holding lines for Adele Gulfo

Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for Adele Gulfo are complete; balances and unit counts will be added when the check is finished.

0gifted (net of own trusts)

Stock options (not counted as shares):

Options held	Strike price	Expires	Intrinsic value (estimate)
50,700	$16.06	Apr 15, 2035	$455K
15,300	$35.45	Jan 7, 2036	$0

Estimate: options held × ($25.03 − strike price), using the most recent insider trade price on Form 4 (Sep 30, 2026), not a market close.

Kamp van der

Director

n/a

Vesting, gifts, unvested awards and holding lines for Kamp van der

Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for Kamp van der are complete; balances and unit counts will be added when the check is finished.

0gifted (net of own trusts)

Stock options (not counted as shares):

Options held	Strike price	Expires	Intrinsic value (estimate)
18,000	$13.26	Apr 1, 2033	$212K
10,000	$11.17	Jan 1, 2034	$139K
32,500	$25.85	Jan 6, 2035	$0
15,300	$35.45	Jan 7, 2036	$0

Estimate: options held × ($25.03 − strike price), using the most recent insider trade price on Form 4 (Sep 30, 2026), not a market close.

John Smither

Director

n/a

−1.6K

n/a

Vesting, gifts, unvested awards and holding lines for John Smither

Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for John Smither are complete; balances and unit counts will be added when the check is finished.

0gifted (net of own trusts)

Stock options (not counted as shares):

Options held	Strike price	Expires	Intrinsic value (estimate)
18,600	$10.22	Jan 14, 2033	$275K
10,000	$11.17	Jan 1, 2034	$139K
32,500	$25.85	Jan 6, 2035	$0
15,300	$35.45	Jan 7, 2036	$0

Estimate: options held × ($25.03 − strike price), using the most recent insider trade price on Form 4 (Sep 30, 2026), not a market close.

William Lewis

Director

n/a

Vesting, gifts, unvested awards and holding lines for William Lewis

Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for William Lewis are complete; balances and unit counts will be added when the check is finished.

0gifted (net of own trusts)

Stock options (not counted as shares):

Options held	Strike price	Expires	Intrinsic value (estimate)
100,000	$12.01	Jan 4, 2034	$1.3M
32,500	$25.85	Jan 6, 2035	$0
15,300	$35.45	Jan 7, 2036	$0

Estimate: options held × ($25.03 − strike price), using the most recent insider trade price on Form 4 (Sep 30, 2026), not a market close.

Mark McKenna

Director

n/a

Vesting, gifts, unvested awards and holding lines for Mark McKenna

Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for Mark McKenna are complete; balances and unit counts will be added when the check is finished.

0gifted (net of own trusts)

Stock options (not counted as shares):

Options held	Strike price	Expires	Intrinsic value (estimate)
72,500	$18.81	Jul 17, 2034	$451K
32,500	$25.85	Jan 6, 2035	$0
15,300	$35.45	Jan 7, 2036	$0

Estimate: options held × ($25.03 − strike price), using the most recent insider trade price on Form 4 (Sep 30, 2026), not a market close.

Robert Gunning

Vice President, Controller

n/a

Vesting, gifts, unvested awards and holding lines for Robert Gunning

Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for Robert Gunning are complete; balances and unit counts will be added when the check is finished.

0gifted (net of own trusts)

Stock options (not counted as shares):

Options held	Strike price	Expires	Intrinsic value (estimate)
14,000	$24.92	Aug 31, 2036	$2K

Estimate: options held × ($25.03 − strike price), using the most recent insider trade price on Form 4 (Sep 30, 2026), not a market close.

Holdings and share of stake for NewAmsterdam Pharma Co N.V. are being verified, so no balances, unit counts or percentages are shown. Sales, proceeds, plan and tax status, titles and dates come straight from individual filings.

What explains the selling$63.3M of sales by plan status, purpose, seller and month

Officer and director open-market sales: $63.3M across 1,970,479 shares. Plan status and stated purpose are separate questions, and a sale can have both.

By plan status

Disclosed plan · $44.7M · 71%

29%

The lighter segment is sales with no plan disclosed in the filing ($18.6M), including tax-related sales outside a plan.

No plan disclosed · $18.5M

Sales with no 10b5-1 plan and no tax reference in the filing. $14.8M of it is Michael Davidson. No plan disclosed is a statement about the filing, not about why the sale happened. Largest such sale: Michael Davidson, Mar 2, 2026

Taxes

$498K of sales (0.8%) cite tax obligations in their footnotes, $458K of them also under a plan. Example: John Smither, Sep 4, 2026

Purchases · 1 buyer (1 trade)

1 officer or director bought shares in this period, in 1 trade(Form 4 code P, leaving out rows the filings describe as reinvested dividends, plan purchases, private deals or moves into the person's own trust). Across all their filings on record there are 4 purchase trades.

Seller	Shares sold	Proceeds	Under a disclosed plan	Share of total	Sales dates
Michael Davidson Chief Executive Officer, Director	762K	$25.3M	42%	40%	Jan 7, 2026 to Mar 2, 2026
Louise Kooij Chief Accounting Officer	503K	$16.8M	100%	26%	Dec 23, 2025 to Jul 20, 2026
Johannes Kastelein Chief Scientific Officer, Director	527K	$15.5M	90%	25%	Jan 5, 2026 to Sep 30, 2026
Mayur Somaiya Chief Financial Officer	105K	$3.4M	100%	5%	Jan 5, 2026 to Jan 21, 2026
Louis Lange Director	73K	$2.2M	0%	3%	Mar 6, 2026 to Mar 11, 2026
John Smither Director	1.6K	$41K	0%	0.1%	Sep 4, 2026 to Sep 4, 2026

Sales by month

Month	Sale proceeds	Disclosed plan	To cover taxes	No plan disclosed
Oct 2025	$0	$0	$0	$0
Nov 2025	$0	$0	$0	$0
Dec 2025	$5.2M	$5.2M	$0	$0
Jan 2026	$8.5M	$8.5M	$0	$0
Feb 2026	$12.2M	$10.6M	$0	$1.6M
Mar 2026	$26.0M	$9.1M	$0	$16.9M
Apr 2026	$0	$0	$0	$0
May 2026	$2.3M	$2.3M	$0	$0
Jun 2026	$1.2M	$1.2M	$0	$0
Jul 2026	$3.2M	$3.2M	$0	$0
Aug 2026	$3.4M	$3.4M	$0	$0
Sep 2026	$1.3M	$1.3M	$41K	$0
Oct 2026	$0	$0	$0	$0

Board members representing outside shareholders (1)Listed and sourced; not part of the management totals or the answer line

Directors whose reported holdings sit mostly in an investment fund or a corporate shareholder they represent, not in their own name, with beneficial ownership disclaimed except for their own financial interest. Listed and sourced here; not part of the management totals or the answer line. Shares a fund hands to its own investors are distributions, not sales.

Board member	Held Oct 13, 2025	Sold	Held Oct 13, 2026	Still held
James Topper ! Holdings and share of stake are being verified. Share-of-stake figures and holdings for this company are held back while they are verified. Sales and other transactions for James Topper are complete. Director	n/a	0	n/a	n/a
Vesting, gifts, unvested awards and holding lines for James Topper Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for James Topper are complete; balances and unit counts will be added when the check is finished. 0gifted (net of own trusts)

Known gaps and uncertainty15 officers and directors not confirmed

Holdings and share of stake are being verified. Balances, unit counts and every share-of-stake figure for NewAmsterdam Pharma Co N.V. are held back until that check is finished. Sales, proceeds, plan and tax status, titles and dates come straight from individual filings and are complete.

External context: we only cite outside events when a documented connection exists. None is shown for this period.

Sources and methodology132 filings on record, 29 filed in the 12-month period, and how we read them

All 132 Forms 3, 4 and 5 on record for NewAmsterdam Pharma Co N.V. (SEC CIK 1936258), filed from Dec 29, 2023 to Oct 2, 2026; 29 of them were filed in the 12 months this page covers, retrieved from SEC EDGAR on Oct 13, 2026. Prices are the ones reported in each filing, often weighted averages.

Holdings. Each holding line (a share class plus an owner, such as a trust or LLC) carries its last reported balance forward. Entities first reported during the period start at zero, so transfers between an insider's own trusts don't count as selling. Lines not reported for three years or more are listed separately and left out of totals.

Sales. A sale counts as under a 10b5-1 plan if its footnote cites one or the filing's Rule 10b5-1 box is checked, and as tax-related if its footnote cites tax obligations or sell-to-cover. Shares withheld by the company for taxes are listed separately. Sales with neither attribute are labeled "no plan disclosed".

Full methodology

Former or inactive filers (6)No filing in 18 months; last reported balances, not in any total

Name	Last filed	Last reported balance
William Jones Jr.	Jan 7, 2025	43,000 shares, last reported balance as of Jan 7, 2025
NAP ForGrowth	Jan 2, 2025	10,656,172 shares, last reported balance as of Dec 30, 2024
Bain Capital Life Sciences Investors, LLC	Dec 17, 2024	10,473,913 shares, last reported balance as of Dec 29, 2023
Hugo Slootweg		No balance on record
Nicholas Downing		No balance on record
Wouter Joustra		No balance on record

Spotted something wrong on this page? Report an error. We check every report against the SEC filing and list what we fix in the corrections log.

NewAmsterdam Pharma Co N.V. insiders sold $63.3M in the past 12 months. How much of their stake is that?

What stands out

Who sold, and how much of their stake

Selling by month

Recent activity

Outside holders, reported separately

Common questions

Is the NewAmsterdam Pharma Co N.V. CEO selling stock?

Why are NewAmsterdam Pharma Co N.V. insiders selling?

Are any NewAmsterdam Pharma Co N.V. insiders buying?

The evidence

No plan disclosed · $18.5M

Taxes

Purchases · 1 buyer (1 trade)

Sales by month