QuickLinks -- Click here to rapidly navigate through this document

As filed with the Securities and Exchange Commission on September 21, 2010

Registration No. 333-168409

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

---

Amendment No. 2
to

FORM S-1
REGISTRATION STATEMENT UNDER
THE SECURITIES ACT OF 1933

---

ASPEN TECHNOLOGY, INC.
(Exact name of registrant as specified in its charter)

---

---

200 Wheeler Road
Burlington, Massachusetts 01803
(781) 221-6400
(Address, including zip code, and telephone number, including area code, of registrant's principal executive offices)

---

Mark E. Fusco
President and Chief Executive Officer
Aspen Technology, Inc.
200 Wheeler Road
Burlington, Massachusetts 01803
(781) 221-6400
(Name, address, including zip code, and telephone number, including area code, of agent for service)

---

---

          Approximate date of commencement of proposed sale to public: As soon as practicable after this registration statement becomes effective.

          If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933 check the following box:    o

          If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.    o

          If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.    o

          If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.    o

          Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of "large accelerated filer," "accelerated filer" and "smaller reporting company" in Rule 12b-2 of the Exchange Act.

          The registrant hereby amends this registration statement on such date or dates as may be necessary to delay its effective date until the registrant shall file a further amendment which specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933 or until the registration statement shall become effective on such date as the Commission, acting pursuant to said Section 8(a), may determine.

---

Explanatory Note

        Part I of this Registration Statement has been intentionally omitted because this Amendment No. 2 does not effect any changes to the Prospectus. The sole purpose of this Amendment No. 2 is to file Exhibits 1.1, 5.1 and 23.2.

---

PART II
INFORMATION NOT REQUIRED IN PROSPECTUS

Item 13.    Other Expenses of Issuance and Distribution.

        The following table sets forth the various expenses to be incurred by us in connection with the sale and distribution of the shares of common stock being registered hereby. All amounts shown are estimates, except for the SEC registration and the FINRA filing fee.

Item 14.    Indemnification of Directors and Officers.

        Section 102 of the Delaware General Corporation Law allows a corporation to eliminate the personal liability of directors of a corporation to the corporation or its stockholders for monetary damages for a breach of fiduciary duty as a director, except where the director breached his duty of loyalty, failed to act in good faith, engaged in intentional misconduct or knowingly violated a law, authorized the payment of a dividend or approved a stock repurchase in violation of Delaware corporate law or obtained an improper personal benefit. We have included such a provision in our certificate of incorporation, as amended, or the charter.

        Section 145 of the Delaware General Corporation Law provides that a corporation has the power to indemnify a director, officer, employee or agent of the corporation and certain other persons serving at the request of the corporation in related capacities against amounts paid and expenses incurred in connection with an action or proceeding to which he is or is threatened to be made a party by reason of such position, if such person shall have acted in good faith and in a manner he reasonably believed to be in or not opposed to the best interests of the corporation, and, in any criminal proceeding, if such person had no reasonable cause to believe his conduct was unlawful; provided that, in the case of actions brought by or in the right of the corporation, no indemnification shall be made with respect to any matter as to which such person shall have been adjudged to be liable to the corporation unless and only to the extent that the adjudicating court determines that such indemnification is proper under the circumstances.

        Article SEVENTH of our charter provides that no director shall be personally liable for any monetary damages for any breach of fiduciary duty as a director, except to the extent that the Delaware General Corporation Law prohibits the elimination or limitation of liability of directors for breach of fiduciary duty.

        Article EIGHTH of our charter provides that a director or officer shall be indemnified by us against:

        (a)   all expenses (including attorneys' fees), judgments, fines and amounts paid in settlement incurred in connection with any litigation or other legal proceeding (other than an action by or in the right of us) brought against him or her by virtue of his or her position as one of our directors or officers if he or she acted in good faith and in a manner he or she reasonably believed to be in, or not

II-1

---

opposed to, our best interests, and, with respect to any criminal action or proceeding, had no reasonable cause to believe his or her conduct was unlawful; and

        (b)   all expenses (including attorneys' fees) and amounts paid in the settlement incurred in connection with any action by us or in our right brought against him or her by virtue of his or her position as one of our directors or officers if he or she acted in good faith and in a manner he or she reasonably believed to be in, or not opposed to, our best interests, except that no indemnification shall be made with respect to any matter as to which such person shall have been adjudged to be liable to us, unless a court determines that, despite such adjudication but in view of all of the circumstances, he or she is entitled to indemnification of such expenses.

        Notwithstanding the foregoing, to the extent that a director or officer has been successful, on the merits or otherwise, including the dismissal of an action without prejudice, he or she is required to be indemnified by us against all expenses (including attorneys' fees) incurred in connection therewith. Expenses shall be advanced to a director or officer at his or her request, provided that he or she undertakes to repay the amount advanced if it is ultimately determined that he or she is not entitled to indemnification for such expenses.

        Indemnification is required to be made unless we determine that the applicable standard of conduct required for indemnification has not been met. In the event of our determination that the director or officer did not meet the applicable standard of conduct required for indemnification, or if we fail to make an indemnification payment within sixty days after such payment is claimed by such person, such person is permitted to petition the court to make an independent determination as to whether such person is entitled to indemnification. As a condition precedent to the right of indemnification, the director or officer must give us notice of the action for which indemnity is sought and we have the right to participate in such action or assume the defense thereof.

        Article EIGHTH of the charter further provides that the indemnification provided therein is not exclusive, and provides that in the event that the Delaware General Corporation Law is amended to expand the indemnification permitted to directors or officers we must indemnify those persons to the fullest extent permitted by such law as so amended.

        We have purchased directors' and officers' liability insurance, which may indemnify our directors and officers against damages arising out of certain kinds of claims that might be made against them based on their negligent acts or omissions while acting in their capacities as such.

Item 15.    Recent Sales of Unregistered Securities.

        We have not made any sales of securities unregistered under the Securities Act within the past three years.

II-2

---

Item 16.    Exhibits and Financial Statement Schedules.

(a)

Exhibits

II-3

---

II-4

---

II-5

---

II-6

---

II-7

---

II-8

---

II-9

---

II-10

---

II-11

---

(b)

Financial Statement Schedules

        All schedules are omitted because they are not required or the required information is shown in the consolidated financial statements or notes thereto.

Item 17.    Undertakings.

        Insofar as indemnification for liabilities arising under the Securities Act of 1933 may be permitted to directors, officers and controlling persons of the registrant pursuant to the foregoing provisions, or otherwise, the registrant has been advised that in the opinion of the Securities and Exchange Commission such indemnification is against public policy as expressed in the Act and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by the registrant of expenses incurred or paid by a director, officer or controlling person of the registrant in the successful defense of any action, suit or proceeding) is asserted by such director, officer or controlling person in connection with the securities being registered, the registrant will, unless in the opinion of its counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question whether such indemnification by it is against public policy as expressed in the Act and will be governed by the final adjudication of such issue.

        The undersigned registrant hereby undertakes that:

        (1)   For purposes of determining any liability under the Securities Act of 1933, the information omitted from the form of prospectus filed as part of this registration statement in reliance upon Rule 430A and contained in a form of prospectus filed by the registrant pursuant to Rule 424(b)(1) or (4) or 497(h) under the Securities Act shall be deemed to be part of this registration statement as of the time it was declared effective.

        (2)   For the purpose of determining any liability under the Securities Act of 1933, each post-effective amendment that contains a form of prospectus shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

II-12

---

SIGNATURES

        Pursuant to the requirements of the Securities Act of 1933, the registrant has duly caused this Amendment No. 2 to the registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Burlington, Commonwealth of Massachusetts, as of September 21, 2010.

        Pursuant to the requirements of the Securities Act of 1933 this Amendment No. 2 to the registration statement has been signed by the following persons in the capacities indicated as of September 21, 2010.

II-13

---

II-14

---

EXHIBIT INDEX

---

---

---

---

---

---

---

---

---

---

---

QuickLinks

Explanatory Note
PART II INFORMATION NOT REQUIRED IN PROSPECTUS

Item 13. Other Expenses of Issuance and Distribution.
Item 14. Indemnification of Directors and Officers.
Item 15. Recent Sales of Unregistered Securities.
Item 16. Exhibits and Financial Statement Schedules.
Item 17. Undertakings.

EXHIBIT INDEX