Note 5 - Summary of Significant Accounting Policies	3 Months Ended
Mar. 31, 2016
Notes to Financial Statements
Significant Accounting Policies [Text Block]	5. Summary of Significant Accounting Policies Principles of consolidation The accompanying condensed consolidated financial statements include the assets, liabilities and expenses of Sun BioPharma, Inc. and our wholly-owned subsidiaries. All significant intercompany transactions and balances have been eliminated in consolidation. Use of estimates The preparation of condensed consolidated financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amount of revenues and expenses during the reporting period. Actual results could differ from those estimates. Debt issuance costs Costs associated with the issuance of debt instruments are capitalized and presented as a direct deduction from the carrying amount of the related debt liability. These costs are amortized on a straight-line basis, which approximates the effective interest method, over the term of the debt agreements and are included in interest expense. Research and development costs Research and development costs to date have consisted primarily of expenses incurred for third-party service providers monitoring and accumulating data related to our preclinical and clinical studies; sponsored research agreements; developing and scaling the manufacturing process necessary to produce sufficient amounts of SBP-101 for use in our pre-clinical studies and human clinical trials; consulting resources with specialized expertise related to execution of our development plan for our SBP-101 product candidate; and costs to license and maintain our licensed intellectual property. Moving forward, research and development expenditures will shift to focus on costs related to the execution of human clinical trials and related efforts to obtain regulatory approval for SBP-101. We charge research and development costs, including clinical trial costs, to expense when incurred. Our human clinical trials are, and will be, performed at clinical trial sites and are administered jointly by us with assistance from contract research organizations (“CROs”). Costs of setting up clinical trial sites are accrued upon execution of the study agreement. Expenses related to the performance of clinical trials generally are accrued based on contracted amounts and the achievement of agreed upon milestones, such as patient enrollment, patient follow-up, etc. We monitor levels of performance under each significant contract, including the extent of patient enrollment and other activities through communications with the clinical trial sites and CROs, and adjust the estimates, if required, on a quarterly basis so that clinical expenses reflect the actual effort expended at each clinical trial site and by each CRO. All material CRO contracts are terminable by us upon written notice and we are generally only liable for actual effort expended by the CROs and certain non-cancelable expenses incurred at any point of termination We expense costs associated with obtaining licenses for patented technologies when it is determined there is no alternative future use of the intellectual property subject to the license. Fair Value Determination of the Company’s Common Stock Prior to becoming a public company, determining the fair value per share or our common stock for use in estimating the fair values of share based payments required making complex and subjective judgments. The Company used the implied valuations based upon the terms from our sales of convertible notes payable to estimate our enterprise value for the dates on which these transactions occurred. The estimated enterprise values considered certain discounts related to control and lack of marketability. Our board of directors also considered the estimated fair value of our common stock in relation to a number of objective and subjective factors, including external market conditions affecting the biotechnology industry sector. Our board of directors also retained an independent financial valuation firm to provide independent estimates of our enterprise value. Until an active trading market develops for our common stock, estimating the fair value per share of our common stock will continue to be highly subjective. There is inherent uncertainty in these estimates. Share-based compensation Share-based incentive awards are accounted for under the provisions of FASB ASC 718, Compensation — Stock Compensation, which requires companies to measure and recognize the cost of employee and non-employee services received in exchange for awards of equity instruments based on the grant date fair value of those awards. Compensation cost is recognized ratably using the straight-line attribution method over the expected vesting period, which is considered to be the requisite service period. The fair value of share-based awards is estimated at the date of grant using the Black-Scholes option pricing model. Risk free interest rates are based upon U.S. Treasury rates appropriate for the expected term of each award. Expected volatility is based primarily on the volatility rates of a set of guideline companies, which consist of public and recently public biotechnology companies. The assumed dividend yield is zero, as we do not expect to declare any dividends in the foreseeable future. The expected term of options granted is determined using the “simplified” method. Under this approach, the expected term is presumed to be the mid-point between the average vesting date and the end of the contractual term. Foreign currency translation adjustments The functional currency of Sun BioPharma Australia Pty Ltd is the Australian Dollar (“AUD”). Accordingly, assets and liabilities, and equity transactions of Sun BioPharma Australia Pty Ltd are translated into U.S. dollars at period-end exchange rates. Revenues and expenses are translated at the average exchange rate in effect for the period. The resulting translation gains and losses are recorded as a component of accumulated comprehensive loss presented within the shareholders’ deficit. During the three-month periods ended March 31, 2016 and 2015, any reclassification adjustments from accumulated other comprehensive loss to operations was inconsequential.

5. Summary of Significant Accounting Policies

Principles of consolidation

The accompanying

condensed

consolidated financial statements include the assets, liabilities and expenses of Sun BioPharma, Inc. and our wholly-owned subsidiaries. All significant intercompany transactions and balances have been eliminated in consolidation.

Use of estimates

The preparation of

condensed

consolidated financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the

condensed

consolidated financial statements and the reported amount of revenues and expenses during the reporting period. Actual results could differ from those estimates.

Debt issuance costs

Costs associated with the issuance of debt instruments are capitalized and presented as a direct deduction from the carrying amount of the related debt liability. These costs are amortized on a straight-line basis, which approximates the effective interest method, over the term of the debt agreements and are included in interest expense.

Research and development costs

Research and development costs to date have consisted primarily of expenses incurred for third-party service providers monitoring and accumulating data related to our preclinical and clinical studies; sponsored research agreements; developing and scaling the manufacturing process necessary to produce sufficient amounts of SBP-101 for use in our pre-clinical studies and human clinical trials; consulting resources with specialized expertise related to execution of our development plan for our SBP-101 product candidate; and costs to license and maintain our licensed intellectual property. Moving forward, research and development expenditures will shift to focus on costs related to the execution of human clinical trials and related efforts to obtain regulatory approval for SBP-101.

We charge research and development costs, including clinical trial costs, to expense when incurred. Our human clinical trials are, and will be, performed at clinical trial sites and are administered jointly by us with assistance from contract research organizations (“CROs”). Costs of setting up clinical trial sites are accrued upon execution of the study agreement. Expenses related to the performance of clinical trials generally are accrued based on contracted amounts and the achievement of agreed upon milestones, such as patient enrollment, patient follow-up, etc. We monitor levels of performance under each significant contract, including the extent of patient enrollment and other activities through communications with the clinical trial sites and CROs, and adjust the estimates, if required, on a quarterly basis so that clinical expenses reflect the actual effort expended at each clinical trial site and by each CRO.

All material CRO contracts are terminable by us upon written notice and we are generally only liable for actual effort expended by the CROs and certain non-cancelable expenses incurred at any point of termination

We expense costs associated with obtaining licenses for patented technologies when it is determined there is no alternative future use of the intellectual property subject to the license.

Fair Value Determination of the Company’s Common Stock

Prior to becoming a public company, determining the fair value per share or our common stock for use in estimating the fair values of share based payments required making complex and subjective judgments. The Company used the implied valuations based upon the terms from our sales of convertible notes payable to estimate our enterprise value for the dates on which these transactions occurred. The estimated enterprise values considered certain discounts related to control and lack of marketability.

Our board of directors also considered the estimated fair value of our common stock in relation to a number of objective and subjective factors, including external market conditions affecting the biotechnology industry sector. Our board of directors also retained an independent financial valuation firm to provide independent estimates of our enterprise value. Until an active trading market develops for our common stock, estimating the fair value per share of our common stock will continue to be highly subjective. There is inherent uncertainty in these estimates.

Share-based compensation

Share-based incentive awards are accounted for under the provisions of FASB ASC 718, Compensation — Stock Compensation, which requires companies to measure and recognize the cost of employee and non-employee services received in exchange for awards of equity instruments based on the grant date fair value of those awards. Compensation cost is recognized ratably using the straight-line attribution method over the expected vesting period, which is considered to be the requisite service period.

The fair value of share-based awards is estimated at the date of grant using the Black-Scholes option pricing model. Risk free interest rates are based upon U.S. Treasury rates appropriate for the expected term of each award. Expected volatility is based primarily on the volatility rates of a set of guideline companies, which consist of public and recently public biotechnology companies. The assumed dividend yield is zero, as we do not expect to declare any dividends in the foreseeable future. The expected term of options granted is determined using the “simplified” method. Under this approach, the expected term is presumed to be the mid-point between the average vesting date and the end of the contractual term.

Foreign currency translation adjustments

The functional currency of Sun BioPharma Australia Pty Ltd is the Australian Dollar (“AUD”). Accordingly, assets and liabilities, and equity transactions of Sun BioPharma Australia Pty Ltd are translated into U.S. dollars at period-end exchange rates. Revenues and expenses are translated at the average exchange rate in effect for the period. The resulting translation gains and losses are recorded as a component of accumulated comprehensive loss presented within the shareholders’ deficit. During the three-month periods ended March 31, 2016 and 2015, any reclassification adjustments from accumulated other comprehensive loss to operations was inconsequential.