Trading Arrangements, by Individual Trading Arrangements, by Individual [Table] Income before interest income and income taxes Income (Loss) From Continuing Operations Before Interest Income, Income Taxes, Noncontrolling Interests Income (Loss) From Continuing Operations Before Interest Income, Income Taxes, Noncontrolling Interests Trading Arrangement: Trading Arrangement [Axis] Maximum Maximum [Member] First 4% of Employee Elective Deferral Matching Contribution, Portion 1 [Member] Matching Contribution, Portion 1 Statistical Measurement [Domain] Statistical Measurement [Domain] Title of 12(b) Security Title of 12(b) Security Document Fiscal Year Focus Document Fiscal Year Focus Subscription period (in years) Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Initial base rent per month Lessee, Operating Lease, Liability, To Be Paid, Per Month Lessee, Operating Lease, Liability, To Be Paid, Per Month Adjustment to Compensation, Amount Adjustment to Compensation Amount Financial Instrument [Axis] Financial Instrument [Axis] Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Customer [Axis] Customer [Axis] Class A common stock, $0.0001 par value; 2,000,000 shares authorized as of June 30, 2026 and December 31, 2025; 40,337 issued and 40,325 outstanding at June 30, 2026 and 40,368 issued and outstanding at December 31, 2025, respectively Class B common stock, $0.0001 par value; 30,000 shares authorized as of June 30, 2026 and December 31, 2025; 6,399 and 6,260 issued and outstanding at June 30, 2026 and December 31, 2025, respectively Common Stock, Value, Issued Schedule of Restricted Stock Unit Activity Share-Based Payment Arrangement, Restricted Stock and Restricted Stock Unit, Activity [Table Text Block] Taxes paid related to net-share settlement of share-based compensation awards Payment, Tax Withholding, Share-Based Payment Arrangement Loss contingency accrual Loss Contingency Accrual Restatement Determination Date Restatement Determination Date Maturities and paydowns of investments Proceeds from Sale, Maturity and Collection of Investments William "Bing" Gordon June 2026 Plan [Member] William "Bing" Gordon June 2026 Plan Schedule of Effective Income Tax Rate Reconciliation Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Release of restricted stock units (in shares) Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures Allowance for credit losses Accounts Receivable, Allowance for Credit Loss Amendment Flag Amendment Flag Current liabilities Liabilities, Current [Abstract] Share price (in usd per share) Shares Acquired, Average Cost Per Share Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Schedule of Net Unrealized Gains (Losses), and Fair Value by Major Security Type for Our Investments Fair Value, Liabilities Measured on Recurring and Nonrecurring Basis [Table Text Block] Asset-backed securities Asset-Backed Securities [Member] Adjustment to Non-PEO NEO Compensation Footnote Adjustment to Non-PEO NEO Compensation Footnote [Text Block] Property, Plant, and Equipment [Abstract] Entity Address, State or Province Entity Address, State or Province Granted (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Gross PEO Total Compensation Amount PEO Total Compensation Amount Common stock, par value (in usd per share) Common Stock, Par or Stated Value Per Share Intangible assets, net Intangible assets, net Intangible Asset, Excluding Goodwill, after Accumulated Amortization Beginning balance (in shares) Ending balance (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number Weighted-average shares in computing net income per share attributable to Class A and Class B common stockholders, basic (in shares) Weighted Average Number of Shares Outstanding, Basic Defined Contribution Plan, Matching Contribution [Domain] Defined Contribution Plan, Matching Contribution, Portion [Domain] Defined Benefit Plan, Matching Contribution [Domain] Accretion on marketable securities, net Accretion (Amortization) of Discounts and Premiums, Investments Long-term investments Long-Term Investments Long-Term Investments Outstanding Aggregate Erroneous Compensation Amount Outstanding Aggregate Erroneous Compensation Amount Amortized Cost Debt Securities, Held-to-Maturity, Amortized Cost, after Allowance for Credit Loss Number of reportable segments Number of Reportable Segments Total current liabilities Liabilities, Current Concentration Risk [Table] Concentration Risk [Table] Noncurrent assets and liabilities Increase (Decrease) in Other Noncurrent Assets and Liabilities, Net Duolingo English Test English Test [Member] English Test Entity Address, City or Town Entity Address, City or Town Granted (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items] Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Statement of Financial Position [Abstract] Document Information [Line Items] Document Information [Line Items] Award Timing MNPI Disclosure Award Timing MNPI Disclosure [Text Block] Released (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period Basis of Presentation and Accounting Principles Basis of Accounting, Policy [Policy Text Block] Deferred cost of revenues Increase (Decrease) In Capitalized Contract Costs, Net Increase (Decrease) In Capitalized Contract Costs, Net Class of Stock [Axis] Class of Stock [Axis] Peer Group Total Shareholder Return Amount Peer Group Total Shareholder Return Amount Period of letter of credit (in months) Letter Of Credit, Period Of Monthly Rent Letter Of Credit, Period Of Monthly Rent Revenue from Contract with Customer Benchmark Revenue from Contract with Customer Benchmark [Member] Less: accumulated amortization Intangible Asset, Finite-Lived, Accumulated Amortization Level 2 Fair Value, Inputs, Level 2 [Member] Total Shareholder Return Vs Peer Group Total Shareholder Return Vs Peer Group [Text Block] Non-Rule 10b5-1 Arrangement Terminated Non-Rule 10b5-1 Arrangement Terminated [Flag] Board of Directors Chairman Board of Directors Chairman [Member] Concentration Risk Type [Axis] Concentration Risk Type [Axis] Impairment of long-lived assets Long-Lived Asset, Excluding Intangible Asset and Goodwill, Impairment and Disposal [Policy Text Block] Recently Issued Pronouncements Not Yet Adopted and Recently Adopted Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Long-term investments, maturity term (in years) Long-Term Investments, Maturity Term Long-Term Investments, Maturity Term Property and equipment included in Current liabilities Capital Expenditures Incurred but Not yet Paid Deferred revenue Increase (Decrease) in Contract with Customer, Liability Use of Estimates Use of Estimates, Policy [Policy Text Block] Defined contribution plan, employer discretionary contribution amount Defined Contribution Plan, Employer Discretionary Contribution Amount Related and Nonrelated Parties [Axis] Related and Nonrelated Parties [Axis] Disaggregation of Revenue Revenue from Contract with Customer [Policy Text Block] PROPERTY AND EQUIPMENT, NET Property, Plant, and Equipment [Text Block] Supplemental disclosure of noncash investing activities: Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] Document Period End Date Document Period End Date Changes in assets and liabilities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital [Abstract] Forfeited and expired (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Forfeitures and Expirations in Period Net cash used for investing activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation Equity Awards Adjustments, Excluding Value Reported in Compensation Table Equity Awards Adjustments, Excluding Value Reported in the Compensation Table [Member] Security Exchange Name Security Exchange Name Treasury stock, at cost; 12 and 0 shares as of June 30, 2026 and December 31, 2025, respectively. Treasury Stock, Common, Value Short-term investments Debt Securities, Held-to-Maturity, Amortized Cost, after Allowance for Credit Loss, Current Granted (in usd per share) Share-Based Compensation Arrangements by Share-Based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Denominator: Earnings Per Share, Basic, Other Disclosure [Abstract] William "Bing" Gordon December 2025 Plan [Member] William "Bing" Gordon December 2025 Plan Entity Shell Company Entity Shell Company Common Class B Common Class B [Member] Segment Segment Reporting, Policy [Policy Text Block] Schedule of Property and Equipment, Net Property, Plant, and Equipment [Table Text Block] EARNINGS PER SHARE Earnings Per Share [Text Block] Name Outstanding Recovery, Individual Name Earnings Per Share [Abstract] Award Timing, How MNPI Considered Award Timing, How MNPI Considered [Text Block] Document Fiscal Period Focus Document Fiscal Period Focus Peer Group Issuers, Footnote Peer Group Issuers, Footnote [Text Block] Total liabilities Liabilities Trading Symbol Trading Symbol Other indefinite-lived intangible assets Intangible Asset, Excluding Goodwill, Indefinite-Lived Purchase of property and equipment Payments to Acquire Property, Plant, and Equipment Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year [Member] Pension Adjustments Prior Service Cost Pension Adjustments Prior Service Cost [Member] Unrecognized compensation cost, options Share-Based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount Income tax payable Accrued Income Taxes, Current Employer matching contribution, percent of employees' gross pay (in percent) Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay Company Selected Measure Name Company Selected Measure Name Income Tax Disclosure [Abstract] Dr. Luis von Ahn Trading Arrangement, Shares Held By Dr. von Ahn [Member] Dr. Luis von Ahn Trading Arrangement, Shares Held By Dr. von Ahn Landlord incentive included in Other assets Landlord Incentives, Incurred But Not Yet Paid Landlord Incentives, Incurred But Not Yet Paid Concentration Risk [Line Items] Concentration Risk [Line Items] Cash flows from operating activities: Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract] Compensation Amount Outstanding Recovery Compensation Amount Individual: Individual [Axis] Denominator for dilutive net income per common share - weighted-average shares (in shares) Weighted Average Number of Shares Outstanding, Diluted Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Entity Emerging Growth Company Entity Emerging Growth Company Equity Valuation Assumption Difference, Footnote Equity Valuation Assumption 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[Abstract] Minimum Minimum [Member] Expiration Date Trading Arrangement Expiration Date Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Postemployment Benefits [Abstract] Schedule of Disaggregation of Revenue Disaggregation of Revenue [Table Text Block] Class A and Class B Common Stock Class A And Class B Common Stock [Member] Class A And Class B Common Stock Gross Unrealized Gains Debt Securities, Held-to-Maturity, Accumulated Unrecognized Gain Schedule of Intangible Assets Amortization Expense Intangible Asset, Finite-Lived, Amortization Expense [Table Text Block] Income Statement Location [Axis] Location, Statement of Income, Balance [Axis] Non-Rule 10b5-1 Arrangement Adopted Non-Rule 10b5-1 Arrangement Adopted [Flag] Weighted average remaining contractual term (in years), outstanding Share-Based Compensation Arrangement by Share-Based Payment Award, 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program, authorized, amount Share Repurchase Program, Authorized, Amount Document Quarterly Report Document Quarterly Report Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested [Member] Advertising Advertising [Member] Capitalized software development costs Capitalized Cost, Internal-Use Software, Addition Capitalized Cost, Internal-Use Software, Addition Awards Close in Time to MNPI Disclosures, Table Awards Close in Time to MNPI Disclosures [Table Text Block] Equity Component [Domain] Equity Component [Domain] PEO Actually Paid Compensation Amount PEO Actually Paid Compensation Amount Adoption Date Trading Arrangement Adoption Date Total stockholders’ equity Beginning balance Ending balance Equity, Attributable to Parent Other (expense) income, net Nonoperating Income (Expense) Debt Securities, Held-to-Maturity, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration] Debt Securities, Held-to-Maturity, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration] ASSETS Assets [Abstract] Title Trading Arrangement, Individual Title Forgone Recovery due to Disqualification of Tax Benefits, Amount Forgone Recovery due to Disqualification of Tax Benefits, Amount Accounting Policies [Abstract] Restatement does not require Recovery Restatement Does Not Require Recovery [Text Block] Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Insider Trading Policies and Procedures [Line Items] Options outstanding, beginning balance (in shares) Options outstanding, ending balance (in shares) Options outstanding (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Number Fair Value Debt Securities, Held-to-Maturity, Fair Value Interest income Interest Income, Operating Insider Trading Policies and Procedures Adopted Insider Trading Policies and Procedures Adopted [Flag] Founder awards where performance has been met Performance Shares [Member] Prepaid expenses and other current assets Prepaid Expense and Other Assets, Current William "Bing" Gordon [Member] William "Bing" Gordon Forfeited and expired (in usd per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price COMMITMENTS AND CONTINGENCIES Commitments and Contingencies Disclosure [Text Block] Compensation Actually Paid vs. Net Income Compensation Actually Paid vs. Net Income [Text Block] Number of operating segments Number of Operating Segments RSUs outstanding Restricted Stock Units (RSUs) Restricted Stock Units (RSUs) [Member] Entity Central Index Key Entity Central Index Key Less: accumulated depreciation Property, Plant, and Equipment, Accumulated Depreciation, Depletion, and Amortization All Adjustments to Compensation All Adjustments to Compensation [Member] Equity [Abstract] Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year [Member] Income Taxes Income Tax, Policy [Policy Text Block] Net cash provided by operating activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation Accounts Receivable Accounts Receivable [Member] Income Statement [Abstract] Stockholders’ equity Equity, Attributable to Parent [Abstract] Document Transition Report Document Transition Report Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Vendor expenses Salary and Wage, Excluding 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share Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] INTANGIBLE ASSETS Intangible Asset [Text Block] Statement [Line Items] Statement [Line Items] Total assets Assets Schedule of Defined Benefit Plans Disclosures [Table] Defined Benefit Plan [Table] Total compensation cost Share-Based Payment Arrangement, Expense Of Modified Awards Share-Based Payment Arrangement, Expense Of Modified Awards Restricted stock units Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract] Amortized Cost Debt Securities, Held-To-Maturity, Amortized Cost, After Allowance For Credit Loss And Cash Equivalents, At Carrying Value Debt Securities, Held-To-Maturity, Amortized Cost, After Allowance For Credit Loss And Cash Equivalents, At Carrying Value Schedule of Income Statement Location for Compensation Expense Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block] Investment in SAFE Equity Securities without Readily Determinable Fair Value, Amount PEO PEO [Member] Number of grantees affected Share-Based Payment Arrangement, Plan Modification, Number of Grantees Affected Cash and Cash Equivalents [Domain] Cash and Cash Equivalents [Domain] Stock based compensation expense (benefit) Total Share-Based Payment Arrangement, Expense Goodwill Goodwill Forgone Recovery due to Violation of Home Country Law, Amount Forgone Recovery due to Violation of Home Country Law, Amount Stock options exercised (in shares) Exercised (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercises in Period Percentage of letter of credit (in percent) Restricted Cash, Noncurrent As A Percentage of Outstanding Letter Of Credit Restricted Cash, Noncurrent As A Percentage of Outstanding Letter Of Credit Granted (in usd per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Cash Equivalents Cash Equivalents, at Carrying Value Amount from beginning balance recognized into revenue Contract with Customer, Liability, Revenue Recognized Stripe Stripe [Member] Stripe (Accumulated Deficit) Retained Earnings Retained Earnings [Member] Long-term obligation under operating leases Operating Lease, Liability, Noncurrent Total operating expenses Operating Expenses Money market funds Money Market Funds [Member] Forfeited (in usd per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Capitalized software Software, In-Development, Internally Developed, and Purchased [Member] Subscription License and Service [Member] Fair Value Fair Value Measurement, Policy [Policy Text Block] Erroneously Awarded Compensation Recovery Erroneously Awarded Compensation Recovery [Table] Increase (Decrease) in Stockholders' Deficit [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Common stock, shares outstanding (in shares) Common Stock, Shares, Outstanding Award Timing Disclosures [Line Items] Fair Value Debt Securities, Held-To-Maturity, Fair Value And Cash Equivalents, At Carrying Value Debt Securities, Held-To-Maturity, Fair Value And Cash Equivalents, At Carrying Value Corporate debt securities Corporate Debt Securities [Member] Net income per share attributable to Class A and Class B common stockholders, diluted (in usd per share) Diluted income per common share (in usd per share) Earnings Per Share, Diluted Entity Current Reporting Status Entity Current Reporting Status Net cash (used for) provided by financing activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation Total Shareholder Return Amount Total Shareholder Return Amount Taxes paid related to net-share settlement of share-based compensation awards Share-Based Payment Arrangement, Decrease for Tax Withholding Obligation Prepaid expenses and other current assets Increase (Decrease) in Prepaid Expense and Other Assets Amortization expense Intangible Asset, Finite-Lived, Amortization Expense Intangible Asset, Finite-Lived [Line Items] Intangible Asset, Finite-Lived [Line Items] Research and development Research and Development Expense Adjustments to reconcile net income to net cash provided by operating activities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract] Cash flows from financing activities: Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract] Revenues Total revenues Revenue from Contract with Customer, Excluding Assessed Tax Property and equipment, net Total property and equipment, net Property, Plant, and Equipment, after Accumulated Depreciation, Depletion, and Amortization Financial 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Arrangements [Member] Other Performance Measure, Amount Other Performance Measure, Amount Award Timing MNPI Considered Award Timing MNPI Considered [Flag] Income from operations Operating Income (Loss) Next 2% of Employee Elective Deferral Matching Contribution, Portion Two [Member] Matching Contribution, Portion Two Current Fiscal Year End Date Current Fiscal Year End Date Non-PEO NEO Average Total Compensation Amount Non-PEO NEO Average Total Compensation Amount Apple Apple [Member] Apple Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year [Member] Schedule of Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Table] Earnings Per Share, Diluted, by Common Class, Including Two-Class Method [Table] Entity File Number Entity File Number Rule 10b5-1 Arrangement Adopted Rule 10b5-1 Arrangement Adopted [Flag] Numerator: Net Income (Loss) 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Remaining Authorized, Amount Arrangement Duration Trading Arrangement Duration Statement of Stockholders' Equity [Abstract] Local Phone Number Local Phone Number 2021 Employee Stock Purchase Plan 2021 Employee Stock Purchase Plan [Member] 2021 Employee Stock Purchase Plan Deferred cost of revenues Capitalized Contract Cost, Net, Current Entity Address, Postal Zip Code Entity Address, Postal Zip Code Entity Registrant Name Entity Registrant Name Income before income taxes Income before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Insider Trading Policies and Procedures Not Adopted Insider Trading Policies and Procedures Not Adopted [Text Block] Commitments and contingencies (Note 9) Commitments and Contingencies Intangible Asset, Finite-Lived, before Accumulated Amortization Intangible Asset, Finite-Lived, before Accumulated Amortization Total property and equipment Property, Plant, and Equipment, before Accumulated Depreciation, Depletion, and Amortization Changed Peer Group, Footnote Changed Peer Group, Footnote [Text Block] Forgone Recovery due to Expense of Enforcement, Amount Forgone Recovery due to Expense of Enforcement, Amount Executive Category: Executive Category [Axis] Furniture, fixtures and equipment Furniture and Fixtures [Member] LIABILITIES AND STOCKHOLDERS’ EQUITY Liabilities and Equity [Abstract] Other Commitments [Table] Other Commitments [Table] Intangible Asset, Finite-Lived, Class [Domain] Intangible Asset, Finite-Lived, Class [Domain] Weighted average remaining contractual term (in years), exercisable Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Weighted-Average Remaining Contractual Term 2021 Incentive Award Plan 2021 Incentive Award Plan [Member] 2021 Incentive Award Plan Number of tranches Share-Based Payment Arrangement, Plan Modification, Number Of Tranches Modified Share-Based Payment Arrangement, Plan Modification, Number Of Tranches 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