IOU “I owe you”

What Is an IOU?

The IOU concept captures a fundamental distinction in finance: the difference between owning something and having a claim against someone who owns it on your behalf. When you deposit $100 in a bank, you don’t own $100 in cash — you have a $100 IOU from the bank, which promises to return that amount on demand. The bank has lent most of that cash to other people; your “balance” is an entry in the bank’s ledger, not a pile of bills with your name on it.

This IOU structure is how the entire modern banking system works. Banks create money by issuing IOUs (loans) without holding equivalent physical currency in reserve — the fractional reserve system allows banks to have outstanding IOUs far exceeding their physical cash holdings. The system is stable as long as not everyone demands redemption simultaneously — which is exactly what a bank run represents: the collapse of confidence that an IOU will actually be honoured.

In crypto, the IOU nature of exchange balances became painfully visible during the FTX collapse. Customer “balances” on FTX were IOUs — promises that FTX would return the funds on demand. When FTX became insolvent, those IOUs became worthless. Users who had moved their crypto to non-custodial wallets — where they held the actual private keys — had real ownership; those who left funds on FTX had an IOU that the counterparty could no longer honour.

IOUs in Financial Markets

The IOU structure is ubiquitous in finance, often without participants recognising it. Bank deposits are IOUs from the bank (protected up to insurance limits). Brokerage accounts in street name — where the broker holds securities on your behalf — are effectively IOUs from the broker for the securities. Money market fund shares are IOUs from the fund promising to maintain $1 NAV. Stablecoins are IOUs from the issuer promising to maintain the dollar peg and redeem for dollars on demand.

The USDT (Tether) case illustrates IOU risk in crypto: Tether issues dollar-denominated IOUs (USDT tokens) and promises each is backed by $1 in reserves. For years, the composition and existence of those reserves was disputed — if the reserves were inadequate, USDT holders would hold IOUs that couldn’t fully be redeemed. Whether through adequate backing or market confidence, USDT has maintained its peg, but the underlying IOU nature of any stablecoin creates counterparty risk that holding actual dollars or on-chain assets does not.

IOU vs. Direct Ownership

Why Is the IOU Concept Important for Traders?

Recognising the IOU nature of custodial holdings clarifies counterparty risk in a way that “balance” or “account” language obscures. Every exchange balance, every bank account, and every custodied asset is an IOU — and IOUs are only as good as the issuer. This doesn’t mean IOUs are always dangerous; a Federal Reserve-insured bank deposit is an extremely reliable IOU. But the reliability exists because of the regulatory backstop, not inherently.

In crypto, where exchanges operate with varying degrees of regulatory oversight and no deposit insurance, the IOU analysis is more consequential. The standard advice — “not your keys, not your coins” — is the crypto community’s recognition that exchange balances are IOUs, and that IOUs can fail. Sizing crypto holdings in custodial exchanges so that a total loss of exchange IOUs would be survivable is the risk management implication of understanding balances as IOUs rather than direct ownership.

For stablecoins specifically, assessing the quality of the IOU requires understanding what backs it. USDC (Circle) publishes monthly attestations of its reserve composition; USDT (Tether) has been less transparent historically. A stablecoin IOU backed by short-duration US Treasuries is substantially safer than one backed by commercial paper, crypto collateral, or unspecified “other assets.” The IOU framework focuses attention on the right question: what exactly is the issuer promising, and what assets back that promise?

Key Takeaways

• Every exchange balance, bank deposit, and custodied asset is an IOU — a promise of future delivery rather than direct ownership — making counterparty risk an inherent feature of any custodial arrangement, regardless of how “balance” language makes it feel like direct ownership.
• FTX’s November 2022 collapse demonstrated that exchange “balances” are IOUs from the exchange: when FTX became insolvent, customer claims became unsecured creditor claims in bankruptcy proceedings — users with funds in non-custodial wallets retained actual ownership while FTX users held worthless IOUs.
• The fractional reserve banking system is built entirely on IOUs — banks issue deposit IOUs far in excess of their physical cash reserves, creating money through lending; the system is stable as long as redemption demand doesn’t exceed liquidity reserves simultaneously.
• Stablecoin IOUs range significantly in quality: USDC publishes monthly third-party attestations of its treasury reserve backing, while other stablecoins have been less transparent about what exactly backs their redemption promise — the IOU framework directs scrutiny to the right question: what assets back the promise?
• The “not your keys, not your coins” principle is the crypto community’s recognition that exchange balances are IOUs subject to counterparty risk — the practical implication is maintaining only actively traded amounts in exchange IOUs while storing significant holdings in non-custodial wallets where direct ownership eliminates counterparty risk.