There have been no material changes to the Company’s significant accounting policies during the six months ended June 30, 2021, as compared to those disclosed in the Annual Report, other than the adoption of ASU No. 2020-06, Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity, effective January 1, 2021 (see Note 7, “Convertible Senior Notes”).

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.

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, which included the Company’s estimates of credit risks as a result of the coronavirus pandemic (COVID-19 global pandemic). 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 determined the fair value of its convertible senior notes to be $326.6 million at June 30, 2021, and $333.5 million at December 31, 2020, based on Level 2 quoted market prices (see Note 7, “Convertible Senior Notes”). The estimated fair value of certain of the Company’s common stock warrants was determined using the Black-Scholes pricing model as of June 30, 2021 and December 31, 2020 (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 its 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. For lease agreements entered into or reassessed after the adoption of ASC 842, the Company combines lease and non-lease components. Rent expense on noncancellable 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 (see Note 6, “Leases”). 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 condensed consolidated balance sheets. Landlord improvement allowances and other similar lease incentives are recorded as property and equipment and as a reduction of the right-of-use leased assets, and are amortized on a straight-line basis as a reduction to operating lease costs.

During the second quarter of 2021, the Company made an $8.1 million equity investment in a private company, which represented less than 5% of the outstanding equity of that company. The investment is accounted for using the cost method, as the investment does not have a readily determinable fair value, and is included as a component of other long-term assets on the condensed consolidated balance sheet at June 30, 2021.

Finite-lived intangible assets are recorded at cost, net of accumulated amortization and, if applicable, impairment charges. Amortization of finite-lived intangible assets is provided over their estimated useful lives on a straight-line basis. The Company reviews its finite-lived intangible assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. The Company did not recognize any impairment losses during the six months ended June 30, 2021 and 2020.

On June 24, 2020, the Company acquired Sugarmate, Inc. (Sugarmate), the developer of a mobile app designed to help people visualize diabetes therapy data in innovative ways. The Sugarmate acquisition was accounted for as an acquisition of assets in accordance with Accounting Standards Update (ASU) No. 2017-01, Business Combinations (Topic 805) Clarifying the Definition of a Business. Substantially all of the fair value was concentrated in a single identifiable asset, a technology-based intangible asset. The purchased intangible asset is being amortized on a straight-line basis over an estimated useful life of five years. The Company’s results of operations include the operating results of Sugarmate since the date of acquisition, the amounts of which were not material.

Revenue is generated primarily from sales of insulin pumps, disposable cartridges and infusion sets to individual customers with third-party insurance coverage and through a network of 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 to be 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 typically is upon shipment for our distributor arrangements and upon receipt for sales directly to individual customers. 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. When there is no standalone value for the complementary product, 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 June 30, 2021 and December 31, 2020 (in thousands):

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. The Company evaluates 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 the 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.


	Three Months Ended June 30,				Six Months Ended June 30,
	2021		2020		2021		2020
Balance at beginning of period	$	23,169	$	16,761	$	22,075	$	16,724
Provision for warranties issued during the period	8,020		4,844		13,916		9,658
Settlements made during the period	(4,751)		(3,331)		(9,007)		(6,721)
Decrease in warranty estimates	(770)		(451)		(1,316)		(1,838)
Balance at end of period	$	25,668	$	17,823	$	25,668	$	17,823

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 8, “Stockholders’ Equity”). The fair value of restricted stock unit (RSU) awards issued under the 2013 Plan that vest solely based on service is estimated based on the fair market value of the underlying stock on the date of grant. The fair value of RSU awards issued under the 2013 Plan that vest based upon the Company’s actual performance relative to predefined performance metrics is estimated based on the fair market value of the underlying stock on the date of grant and the probability that the specified performance criteria will be met, subject to the awardee’s continuing service through the measurement date. We update our assessment of the probability that the specified performance criteria will be achieved each quarter, and adjust our estimate of the fair value of the performance-based RSUs if necessary.

Basic net income (loss) per share is calculated by dividing the net income (loss) by the weighted average number of common shares outstanding for the period, without consideration for common stock equivalents. Diluted net income per share reflects the potential dilution that would occur if securities exercisable for or convertible into common stock were exercised for or converted into common stock. Dilutive common share equivalents are comprised of stock options and unvested RSUs outstanding under the Company’s stock plans, potential awards to be granted pursuant to the ESPP, and common stock warrants, each calculated using the treasury stock method; and shares issuable upon conversion of the convertible senior notes, calculated using the if-converted method. For common stock 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 June 30, 2020, and the six months ended June 30, 2021 and 2020, there is no difference in the weighted average number of shares used to calculate basic and diluted net loss per share due to the Company’s net loss position. For the three months ended June 30, 2021, the numerator and denominator of the diluted net income per share computation are calculated as follows:


	Three Months Ended June 30,
(in thousands)	2021
Net income - basic and diluted	$	4,008



Weighted average shares outstanding - basic	62,717
Dilutive common share equivalents:
Options to purchase common stock	2,550
Unvested restricted stock units	246
Warrants to purchase common stock	148
Awards to be granted under the ESPP	2
Convertible senior notes (if-converted)	—
Weighted average shares outstanding - diluted	65,663


	Three Months Ended June 30,		Six Months Ended June 30,
	2021	2020	2021	2020
Options to purchase common stock	—	6,195	5,136	5,992
Unvested restricted stock units	—	132	170	132
Warrants to purchase common stock	30	640	251	640
Awards to be granted under the ESPP	—	8	4	4
Convertible senior notes (if-converted)	2,554	1,375	2,554	688
	2,584	8,350	8,115	7,456

In December 2019, the Financial Accounting Standards Board (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 early adopted the new guidance in the second quarter of 2020. As a result, the Company recognized, on a prospective basis, $13,000 of income tax expense in the second quarter of 2020 upon the reversal of tax benefits recorded in the first quarter of 2020 related to unrealized gains on short-term investments.

an Entity’s Own Equity, which is intended to simplify the accounting for convertible instruments. This new guidance eliminates certain models that require separate accounting for embedded conversion features, and eliminates certain of the conditions for equity classification for contracts in an entity’s own equity. Accordingly, a convertible debt instrument will be accounted for as a single liability measured at its amortized cost, as long as no other features require bifurcation and recognition as derivatives. The new guidance can be adopted through either a modified retrospective method of transition or a fully retrospective method of transition. ASU 2020-06 is effective for public business entities for fiscal years beginning after December 15, 2021, including interim periods within those fiscal years. Early adoption is permitted for fiscal years beginning after December 15, 2020, including interim periods within those fiscal years. The Company elected to early adopt the new standard on January 1, 2021 using the modified retrospective method, and recorded a net reduction to accumulated deficit of $9.0 million, a decrease to additional paid-in capital of $85.8 million, and an increase to convertible senior notes, net - long-term of $76.8 million to reflect the impact of the accounting change (see Note 7, “Convertible Senior Notes”).