Your Credit Card Interest Used to Be Tax-Deductible

Imagine a $120 pair of sneakers presented as four payments of $30. The shoes haven't become cheaper. Your next paycheck has become part of the sales pitch.

Buy now, pay later feels like an invention of the smartphone age. Its deeper business idea is much older: help the customer buy before the customer has earned the money.

America once gave that idea a remarkable tax advantage.

In 1979, IRS guidance listed interest on personal debts, credit cards, bank loans, and installment purchases as deductible, subject to exceptions. For taxpayers who itemized and qualified, the government effectively reduced the cost of borrowing to consume. By 1991, personal interest was no longer deductible. IRS historical records, 1991 instructions.

The familiar origin story needs some care. Diners Club introduced its restaurant charge card in 1950; merchant cards existed earlier. And federal installment-credit controls under Regulation W began in 1941, during wartime, rather than the Depression. The Fed suspended them in May 1952. Consumer credit's expansion involved several changes, spread across decades. Federal Reserve history, 1950 card milestone, Regulation W history, 1952 suspension.

The business lesson survives those corrections: financing can expand a company's addressable market without increasing its customers' incomes.

That is why a payment button can also function as a sales tool. Merchants may pay for financing because it helps turn hesitation into a purchase. Affirm's filings describe merchant transaction fees; the CFPB documents how installment lenders pitch additional sales to retailers. Affirm's annual filing, CFPB market study.

Yesterday, a tax deduction lowered borrowing's effective price. Today, installment checkout can lower the immediate cash needed to say yes. Different mechanisms, similar commercial ambition: bring a purchase forward.

Credit can move purchasing power through time. It cannot manufacture the income needed to repay it.

That distinction matters when interpreting consumer spending. A sale financed today is real revenue today. It also creates a claim on money the buyer would otherwise have available later. Strong sales alone cannot tell us whether households are becoming more prosperous.

There is a useful counterargument: spreading payments can be sensible. In the Fed's August 2026 analysis of its 2025 household survey, 82% of BNPL users cited convenience. Yet 26% reported at least one late payment in the prior year. Neither figure justifies treating every borrower as distressed—or every transaction as harmless. Federal Reserve analysis.

For investors evaluating Affirm ($AFRM), my investment claim is that loan growth deserves a premium only when the economics survive funding costs and credit losses. A busy checkout is insufficient evidence of a durable lending business.

For founders, the lesson reaches beyond finance: when removing friction lifts demand, ask which constraint disappeared. Was it inconvenience, or the customer's inability to pay?

The checkout celebrates the sale immediately. The household lives with the repayment schedule.

When financing makes something feel affordable, how much of the growth have we simply borrowed from next month?

Sources and fact verification

Verified October 21, 2026. The seed is used as a historical starting point, rather than reproduced as a verified quotation; its author and original context were not supplied.

• Tax treatment: IRS, Individual Income Tax Returns 1979, Explanation of Terms, tax-year 1979 material, lists deductible personal-debt interest and exceptions. IRS, 1991 Form 1040 Instructions, tax-year 1991, printed p. 5 and Schedule A instructions, explicitly excludes personal interest, including car loans and credit card balances. This was an itemized deduction, not a reimbursement of principal or a benefit automatically received by every borrower. The seed's “all debt” wording is too broad.
• Cards: Federal Reserve, Recent Developments in the Credit Card Market and the Financial Obligations Ratio, Autumn 2005, printed p. 479, dates the Diners Club third-party restaurant charge card to 1950. Federal Reserve History, Electronic Point-of-Sale Payments, 2024, describes earlier merchant cards. That essay dates Diners Club's beginning to 1949; the article uses the Bulletin's specific card-issuance milestone. A charge card is distinct from a revolving balance credit card.
• Credit controls: Federal Reserve Bulletin, November 1950, printed p. 1433, dates Regulation W's introduction to September 1, 1941, with defense production and inflation as the context. Federal Reserve Bulletin, May 1952 records suspension effective May 7, 1952. This does not establish that one deregulation caused all subsequent consumer-credit growth. The seed's payday-loan chronology is omitted because it requires separate evidence.
• Merchant economics: Affirm FY2026 Form 10-K, fiscal year ended June 30, 2026, describes merchant fees, consumer interest, funding costs, and credit-loss provisions. Affirm investor FAQs, undated, accessed October 21, 2026, confirms Nasdaq symbol AFRM. Affirm offers both interest-bearing and 0% products; the article does not imply that all its loans are interest-free pay-in-four loans.
• Sales incentives: CFPB, Buy Now, Pay Later: Market Trends and Consumer Impacts, September 15, 2022, printed pp. 64–65, documents lenders' merchant marketing about incremental sales. Marketing claims do not prove a causal sales lift for every merchant; the article makes no numerical uplift claim.
• Contemporary connection and counterargument: Federal Reserve, Consumer & Community Context, August 19, 2026, using the 2025 Survey of Household Economics and Decisionmaking: 82% of BNPL users cited convenience, and 26% said they paid late at least once in the prior year. These are respondent-level survey measures, not loan default rates or Affirm-specific outcomes. Multiple reasons for use could be selected. The HTML chart placement was corrected September 3, 2026.
• Interpretation: The connection between historical tax incentives and modern checkout design, the future-income framing, and the investment criterion are the author's analysis. The $120 sneakers are an illustrative example. No claim is made that all financed spending would otherwise be lost, or that total spending must fall by an equal amount next month.

Alternative headlines

1. When America Made Credit Card Interest Tax-Deductible
2. Can a Better Checkout Make Us Richer?
3. The Old Business Idea Inside Your Pay-in-Four Button

Recommended visual

header-dark.png and header-light.png — coordinated AI illustrations generated with Higgsfield GPT Image 2.5 Flare. A vintage refrigerator merges with a modern smartphone, with a blank receipt folded into four steps: a conceptual bridge between postwar consumer credit and installment checkout. The dark version uses midnight navy and amber lighting; the light version uses an ivory background and cobalt accents. Both are 2688 × 1520, with the focal objects inside the central 5:2 cover-crop band. header.png is a compatibility copy of the light version. Exact prompts, references, settings, and result URLs are in header-prompt.md. No logos, invented data, or documentary claims. No third-party photograph or clip is used.