The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and judgments that affect the reported amounts of assets, liabilities, revenues and expenses and the disclosure of contingent assets and liabilities in the Company’s consolidated financial statements and accompanying notes as of the date of the consolidated financial statements. Some of those judgments can be subjective and complex, and therefore, actual results could differ materially from those estimates under different assumptions or conditions.

Operating segments are identified as components of an enterprise about which discrete financial information is available for evaluation by the chief operating decision-maker (CODM) in making decisions regarding resource allocation and assessing performance. The Company is organized based on its current product portfolio, which consists primarily of insulin pumps, disposable cartridges and infusion sets for the storage and delivery of insulin. The Company views its operations and manages its business as one segment because key operating decisions and resource allocations are made by the CODM using consolidated financial data.

The Company grants credit to various customers in the ordinary course of business and is paid directly by customers who use the products, distributors and third-party insurance payors. The Company maintains an allowance for its current estimate of expected credit losses. Provisions for expected credit losses are estimated based on historical experience, assessment of specific risk, review of outstanding invoices, forecasts about the future, and various assumptions and estimates that are believed to be reasonable under the circumstances. Uncollectible accounts are written off against the allowance after appropriate collection efforts have been exhausted and when it is deemed that a balance is uncollectible.

The carrying amounts of cash and cash equivalents, accounts receivable, accounts payable, accrued expenses, and employee-related liabilities are reasonable estimates of their fair values because of the short-term nature of these assets and liabilities. Short-term investments are carried at fair value. The Company believes the fair value of its operating lease liabilities at March 31, 2020 approximated their carrying value, based on the borrowing rates that were available for loans with similar terms as of that date. The estimated fair value of certain of the Company’s common stock warrants was determined using the Black-Scholes pricing model as of March 31, 2020 and December 31, 2019 (see Note 5, “Fair Value Measurements”).

Lease right-of-use assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent their obligation to make lease payments arising from the lease. Operating lease right-of-use assets and liabilities are recognized when the Company takes possession of the leased property (the Commencement Date) based on the present value of lease payments over the lease term. Rent expense on noncancelable leases containing known future scheduled rent increases is recorded on a straight-line basis over the term of the respective leases beginning on the Commencement Date. The difference between rent expense and rent paid is accounted for as a component of operating lease right-of-use assets on the Company’s consolidated balance sheet. Landlord improvement allowances and other such lease incentives are recorded as property and equipment and as reduction of the right-of-use leased assets, and are amortized on a straight-line basis as a reduction to operating lease costs. Leases with an initial term of 12 months or less are expensed as incurred and are not recorded as right-of-use assets on the consolidated balance sheets (see Note 6, “Leases”).

Revenue is generated primarily from sales of insulin pumps, disposable cartridges and infusion sets to individual customers and third-party distributors that resell the products to insulin-dependent diabetes customers. The Company recognizes revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the Company expects to be entitled in exchange for those goods or services.

The Company considers the individual deliverables in its product offering as separate performance obligations. The transaction price is determined based on the consideration expected to be received, based either on the stated value in contractual arrangements or the estimated cash to be collected in non-contracted arrangements. The Company allocates the consideration to the individual performance obligations and recognizes the consideration based on when the performance obligation is satisfied, considering whether or not this occurs at a point in time or over time. Generally, insulin pumps, cartridges, infusion sets and accessories are deemed performance obligations that are satisfied at a point in time when the customer obtains control of the promised good, which is upon delivery. Complementary products, such as t:connect and the Tandem Device Updater, are considered performance obligations that are satisfied over time, as access and support for these products is provided throughout the typical four-year warranty period of the insulin pumps. Accordingly, revenue related to the complementary products is deferred and recognized ratably over a four-year period. There is no standalone value for these complementary products. Therefore, the Company determines their value by applying the expected cost plus a margin approach and then allocates the residual to the insulin pumps. Deferred revenue related to these performance obligations that are satisfied over time was included in the following consolidated balance sheet accounts in the amounts shown as of March 31, 2020 and December 31, 2019 (in thousands):

The Company offers a 30-day right of return to customers in the U.S. and Canada from the date of shipment of its insulin pumps, provided a physician’s confirmation of the medical reason for the return is received. Estimated allowances for sales returns are based on historical returned quantities as compared to pump shipments in those same periods of return. The return rate is then applied to the sales of the current period to establish a reserve at the end of the period. The return rates used in the reserve are adjusted for known or expected changes in the marketplace when appropriate. The allowance for sales returns is recorded as a reduction of revenue and an increase in deferred revenue in the period in which the related sale is recorded. The amount recorded in deferred revenue on the Company’s consolidated balance sheets for allowances for sales returns was $0.5 million and $0.4 million at March 31, 2020 and December 31, 2019, respectively. Actual product returns have not differed materially from estimated amounts recorded in the accompanying condensed consolidated financial statements.

The Company generally provides a four-year warranty on its insulin pumps to end-user customers and may replace any pumps that do not function in accordance with the product specifications. Insulin pumps returned to the Company may be refurbished and redeployed. Additionally, the Company offers a six-month warranty on disposable cartridges and infusion sets. Estimated warranty costs are recorded at the time of shipment. We evaluate the reserve quarterly. Warranty costs are primarily estimated based on the current expected product replacement cost and expected replacement rates utilizing historical experience. Recently released versions of the pump may not incur warranty costs in a manner similar to previously released pumps, on which the Company initially bases its warranty estimate of newer pumps. The Company may make further adjustments to the warranty reserve when deemed appropriate, giving additional consideration to length of time the pump version has been in the field and future expectations of performance based on new features and capabilities that may become available through Tandem Device Updater.

Stock-based compensation cost is measured at the grant date based on the estimated fair value of the award, and the portion that is ultimately expected to vest is recognized as compensation expense over the requisite service period on a straight-line basis. The Company estimates the fair value of stock options issued under the Company’s Amended and Restated 2013 Stock Incentive Plan (2013 Plan), and the fair value of the employees’ purchase rights under the Company’s 2013 Employee Stock Purchase Plan (ESPP), using the Black-Scholes option-pricing model on the date of grant. The Black-Scholes option-pricing model requires the use of assumptions about a number of variables, including stock price volatility, expected term, dividend yield and risk-free interest rate (see Note 7, “Stockholders’ Equity”). For awards that vest based on the achievement of service conditions, the Company recognizes expense using the straight-line method less estimated forfeitures based on historical experience.

Basic net loss per share is calculated by dividing the net loss by the weighted average number of common shares that were outstanding for the period, without consideration for common stock equivalents. Diluted loss per share is calculated in accordance with the treasury stock method and reflects the potential dilution that would occur if securities or other contracts to issue common stock were exercised or converted to common stock. Dilutive common share equivalents are comprised of warrants, potential awards granted pursuant to the ESPP, and stock options outstanding under the Company’s equity incentive plans. For warrants that are recorded as a liability in the accompanying condensed consolidated balance sheets, the calculation of diluted loss per share requires that, to the extent the average market price of the underlying shares for the reporting period exceeds the exercise price of the warrants and the presumed exercise of the warrants is dilutive to loss per share for the period, an adjustment is made to net loss used in the calculation to remove the change in fair value of the warrants from the numerator for the period. Likewise, an adjustment to the denominator is required to reflect the related dilutive shares, if any, under the treasury stock method. For the three months ended March 31, 2020 and 2019, there is no difference in the number of shares used to calculate basic and diluted shares outstanding due to the Company’s net loss position.

In June 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which modifies the measurement and recognition of credit losses for most financial assets and certain other instruments. The new standard requires the use of forward-looking expected credit loss models based on historical experience, current conditions, and reasonable and supportable forecasts that affect the collectability of the reported amount, which may result in earlier recognition of credit losses under the new standard. The new standard also requires that credit losses related to available-for-sale debt securities be recorded as an allowance through net income (loss) rather than reducing the carrying amount under the prior, other-than-temporary-impairment model. The new standard must be adopted using the modified retrospective approach and was effective for the Company starting in the first quarter of fiscal 2020. The Company determined there was no cumulative-effect transition adjustment to the opening balance of accumulated deficit for recognition of additional credit losses upon adoption of this standard as of January 1, 2020 based on its outstanding accounts receivable, the composition and credit quality of its short-term investments, and current economic conditions as of that date.

In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement: Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement, which adds and modifies certain disclosure requirements for fair value measurements. Under the new guidance, entities will no longer be required to disclose the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy, or valuation processes for Level 3 fair value measurements. However, public companies will be required to disclose the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements, and related changes in unrealized gains and losses included in other comprehensive income. The updated guidance was effective for the Company starting in the first quarter of fiscal 2020. As a result, the Company modified certain fair value measurement disclosures primarily related to its Level 3 liabilities (see Note 5, “Fair Value Measurements”).

In December 2019, the FASB issued ASU No. 2019-12, Simplifying the Accounting for Income Taxes, which is intended to simplify various aspects of the income tax accounting guidance, including requirements such as tax basis step-up in goodwill obtained in a transaction that is not a business combination, ownership changes in investments, and interim-period accounting for enacted changes in tax law. ASU 2019-12 is effective for public business entities for fiscal years beginning after December 15, 2020, including interim periods within those fiscal years, and early adoption is permitted. The Company is in the process of assessing the impact of the adoption of the standard on its consolidated financial statements.