Additional Public Offering vs Secondary Offering: Key Differences

The table compares them on definition, who sells, where the money goes, the effect on the share count, who uses each, legal and tax treatment, risk, liquidity and a typical example.

The names get mixed up in the press. Reports often call any offering after an IPO “secondary,” even when the company sells new shares. In the strict sense, a secondary offering is a sale by existing holders. An additional offering, or follow-on, is a sale of new shares by the company.

The prospectus settles it in two places. The cover says who is selling: “we are offering” means new shares, and “the selling stockholders are offering” means existing ones. The Use of Proceeds section says who keeps the money. Some deals combine both, with separate share counts for each side.

Tax follows the same split. A company owes no tax when it receives cash for its own stock (26 U.S.C. 1032). A selling holder has a gain or loss on the shares sold, measured against what they paid.

An APO: Rapport Therapeutics

On September 9, 2025, the Nasdaq-listed drug developer sold 9,615,385 new shares at $26.00. That raised $250 million before the banks’ fee of $15 million, or 6%. The company said it would use most of the money for clinical trials (Rapport prospectus). The shares came off a Form S-3 shelf, a registration filed in advance so a company can sell when it chooses.

• Shares outstanding36,497,677 → 46,113,062, +26%
• A holder with 1% before1.00% → 0.79% of the company
• InsidersDirectors and officers agreed not to sell for 90 days

A Secondary: Diversified Energy

On September 16, 2025, funds that held Diversified Energy shares sold 5,713,353 of them at $13.75, about $78.6 million. The sellers kept $13.20 a share, $75.4 million in total, and the banks kept the rest. The company, listed on the NYSE and in London, received nothing. Its prospectus said the sale would not dilute existing holders (Diversified prospectus).

Both kinds of sale need an SEC registration statement and a prospectus. Most follow-ons by established companies use Form S-3, a short form for companies that have reported to the SEC for at least 12 months. A company with $75 million or more of stock held by outside investors can sell new shares off the shelf without a size cap (Form S-3). A smaller one can sell no more than a third of that amount in any 12 months.

Larger companies get more room. A company with $700 million of stock held by outside investors is a well-known seasoned issuer (Rule 405), with added flexibility in how and when it registers. In a secondary, the sellers often hold restricted stock. Registering the sale lets them sell a large block at once, outside the limits of Rule 144.

Banks run most of these deals the way they run an IPO. They gather orders, a process called book-building, and often get an option to sell extra shares, known as a greenshoe. Diversified Energy’s banks had an option on 857,002 more shares, also from the sellers.

Additional Public Offering

For

Raises cash without new debt. A shelf lets the company move quickly. The new money stays in the business.

Against

Dilutes every existing holder. Bank fees of several percent. The market may read the raise as a sign the company needs cash.

Verdict: an APO makes sense when the company has a clear use for the money. For a shareholder, the question is whether that use will earn more than the dilution costs. Read the Use of Proceeds section before you judge it.

Secondary Offering

For

No dilution. Large holders can exit in one orderly sale. More shares in public hands can make trading deeper.

Against

The company gets nothing. A big block can push the price down for a while. Insider selling can unsettle other holders.

Verdict: a secondary changes who owns the company and leaves the company itself unchanged. For other holders, the effect is mostly on supply and sentiment. Check who is selling and what share of their stake they are selling.

If you own shares in a public company, an APO cuts your percentage. Your dollar value depends on the price and on what the company does with the cash. The mechanics are covered in dilution. A secondary leaves your percentage alone, but extra supply can move the price for a few days.

If you invested before an IPO, a secondary offering is one way large holders sell after the listing. It often follows the end of the IPO lock-up, the period when insiders agree not to sell. If you hold through a fund or SPV, its manager decides whether to join. A private sale of shares before an IPO is a different thing, covered in secondary transactions.

Common Mistakes

• Assuming every “secondary” is non-dilutiveThe press uses the word loosely. Check the prospectus cover for “we are offering.”
• Reading insider selling as bad newsFunds often sell because a lock-up has ended or the fund is near the end of its life. Look at the reason and the size.
• Ignoring the use of proceedsIn an APO, the case for dilution sits in that section. Read it.
• Confusing a secondary offering with a private secondaryOne is a public, registered sale. The other is a private trade in a company’s shares, usually before an IPO.

Additional public offering (APO)

A sale of new shares by a company that is already listed. Also called a follow-on.

Secondary offering

A registered public sale of existing shares by current holders. The company receives none of the money.

Selling stockholders

The holders named in a prospectus who sell their own shares in an offering.

Dilution

The drop in each holder’s percentage of a company when it issues new shares.

Use of proceeds

The prospectus section that says who receives the money and how the company plans to spend its part.

Form S-3

A short SEC registration form for companies that have reported for at least 12 months.

Shelf registration

A registration filed in advance, so a company can sell securities later when it chooses.

Public float

The value of a company’s stock held by investors outside the company’s insiders.

Well-known seasoned issuer

Under SEC rules, generally a company with at least $700M of stock held by outside investors.

Greenshoe

An option for the banks to sell extra shares in an offering when demand is strong.

Lock-up

An agreement by insiders not to sell for a set period after an offering.

Figures were last checked on November 6, 2026. Deal figures come from the companies’ prospectus supplements on SEC EDGAR. Percentages are calculated from those figures. All rules described are US rules.