Exhibit 5.1

Calise Y. Cheng

+1 650 843 5172

ccheng@cooley.com

June 1, 2018

Adaptive Insights, Inc.

3350 W. Bayshore Road, Suite 200

Palo Alto, CA 94303

Ladies and Gentlemen:

We have acted as counsel to Adaptive Insights, Inc., a Delaware corporation (the “Company”), in connection with the filing by the Company of a Registration Statement (No. 333-224996) on Form S-1 (the “Registration Statement”) with the Securities and Exchange Commission, including a related prospectus filed with the Registration Statement (the “Prospectus”), covering an underwritten public offering (the “Offering”) of up to 9,430,000 shares of the Company’s Common Stock, par value $0.001 per share (the “Shares”), which includes (i) up to 9,050,000 Shares that may be sold by the Company (including up to 1,230,000 Shares that may be sold by the Company pursuant to the exercise of an option to purchase additional Shares granted to the underwriters) (collectively, the “Company Shares”) and (ii) 380,000 Shares to be sold by the selling stockholders identified in such Registration Statement (the “Stockholder Shares”).

In connection with this opinion, we have (i) examined and relied upon (a) the Registration Statement and related Prospectus, (b) the Company’s Amended and Restated Certificate of Incorporation and Amended and Restated Bylaws, as currently in effect as of the date hereof, (c) the Company’s Amended and Restated Certificate of Incorporation, filed as Exhibit 3.3 to the Registration Statement (the “Revised Certificate of Incorporation”) and the Company’s Amended and Restated Bylaws, filed as Exhibit 3.4 to the Registration Statement, each of which will be in effect upon the closing of the Offering, and (d) the originals or copies certified to our satisfaction of such records, documents, certificates, memoranda and other instruments as in our judgment are necessary or appropriate to enable us to render the opinion expressed below and (ii) assumed that the Board of Directors of the Company or the Pricing Committee thereof has taken action to set the sale price of the Shares.

We have assumed the genuineness and authenticity of all documents submitted to us as originals, and the conformity to originals of all documents submitted to us as copies and the due execution and delivery, other than by the Company, of all documents where due execution and delivery are prerequisites to the effectiveness thereof. As to certain factual matters, we have relied upon a certificate of an officer of the Company and have not sought to independently verify such matters. Our opinion is expressed only with respect to the General Corporation Law of the State of Delaware. We express no opinion to the extent that any other laws are applicable to the subject matter hereof and no opinion and provide no assurance as to compliance with any federal or state securities law, rule or regulation.

On the basis of the foregoing, and in reliance thereon, we are of the opinion that (i) the Company Shares, when sold and issued as described in the Registration Statement and the related Prospectus, will be validly issued, fully paid and non-assessable, and (ii) the Stockholder Shares have been validly issued and are fully paid and non-assessable.

Cooley LLP 3175 Hanover Street Palo Alto, CA 94304-1130

t: (650) 843-5000 f: (650) 849-7400 cooley.com

We consent to the reference to our firm under the caption “Legal Matters” in the Prospectus included in the Registration Statement and to the filing of this opinion as an exhibit to the Registration Statement.

Sincerely,

COOLEY LLP

Cooley LLP 3175 Hanover Street Palo Alto, CA 94304-1130

t: (650) 843-5000 f: (650) 849-7400 cooley.com