> ## Content Index
> Fetch the complete content index at: https://altcoininvestor.com/llms.txt
> Use this file to discover other available public pages before exploring further.

# How Stablecoins Actually Hold Their Peg
- URL: https://altcoininvestor.com/how-do-stablecoins-work-2/
- Published: 2026-09-08T21:05:46.000Z
- Updated: 2026-09-08T21:05:47.000Z
- Description: Fiat reserves, crypto collateral, or algorithmic code. Three mechanisms, three risk profiles. Terra/Luna showed what happens when the mechanism is reflexive.
- Author: Charles Perrin
- Tags: Stablecoins, DeFi, Stablecoin Income, Beginner, Passive Income

## The Question: What Keeps a Stablecoin Stable?

![Fiat reserves and Treasury bills backing stablecoin redemption mechanisms](https://cdn.getmidnight.com/13448471d89a9cd8d7f71026a0334ec8/2026/09/stablecoin-peg-mechanisms-explained-after-h2-1.webp)

The stablecoin market held $270 billion in assets as of April 2026\. Tether's USDT accounts for $189.6 billion of that, Circle's USDC for $77.6 billion, and MakerDAO's DAI for $4.7 billion. Each of these tokens trades at or near one dollar. The question most new holders never ask - and the one that matters most - is what mechanism actually keeps that peg in place.

A stablecoin does not hold its peg through physics or law. It holds because of a credible promise: that you can exchange one token for one dollar's worth of value at any time. The mechanism backing that promise varies. Fiat-backed stablecoins hold bank deposits and Treasury bills. Crypto-collateralized stablecoins lock digital assets in smart contracts that liquidate when collateral falls below a threshold. Algorithmic stablecoins try to maintain the peg through supply-and-demand arbitrage without holding reserves at all.

Each mechanism has a different breaking point. The eurozone sovereign debt crisis taught European bond markets that a promised yield is only real if the underlying credibility holds. When Greek bond yields hit 30% in 2011, those were not returns - they were the market pricing in default risk. The same principle applies to stablecoins. When the peg breaks, you discover whether the mechanism backing it was ever sound.

## Fiat-Backed Stablecoins: Reserve Redemption

![Overcollateralized crypto assets securing stablecoin debt positions in smart contracts](https://cdn.getmidnight.com/13448471d89a9cd8d7f71026a0334ec8/2026/09/stablecoin-peg-mechanisms-explained-after-h2-2.webp)

Fiat-collateralized stablecoins are the simplest model. For every token in circulation, the issuer holds one dollar in a bank account or short-term Treasury bill. USDC and USDT operate this way. The peg is maintained through a redemption mechanism: authorized participants can burn one token and receive one dollar, or deposit one dollar and mint one token. Retail users almost never touch this primary market. They buy and sell on exchanges, where arbitrageurs keep the secondary price close to one dollar by exploiting any gap between the market price and the redemption window.

Circle publishes monthly attestations of USDC reserves and discloses that the majority sits in the Circle Reserve Fund, with the rest held as cash at regulated banks. Tether shifted its reserves heavily toward US Treasury bills over the last three years. As of Q1 2026, Tether's quarterly attestation shows a $113 billion Treasury position. The quality of these reserves matters. Not all dollar-backed stablecoins hold the same assets, and not all bank deposits carry the same risk.

The mechanism broke visibly in March 2023 when Silicon Valley Bank collapsed. Circle had disclosed that $3.3 billion of USDC's reserves were held at SVB. USDC fell to $0.87 on secondary markets as holders rushed to exit before Circle could clarify whether those deposits were recoverable. The peg returned within 48 hours after the US government announced it would backstop all SVB deposits, but the depeg showed that fiat-backed stablecoins are vulnerable to counterparty risk - specifically, the risk that the bank holding the reserves fails before the issuer can redeem them.

The Terra crisis in May 2022 produced a different kind of contagion. As confidence in algorithmic stablecoins collapsed, holders rotated into fiat-backed alternatives. Tether dropped briefly to $0.97 during peak selling pressure, while USDC rose to $1.01 and BUSD rose to $1.0149\. The deviation was temporary, but it revealed that even the most liquid stablecoins experience secondary-market stress when systemic confidence breaks.

Fiat-backed stablecoins fail when reserves are inadequate, inaccessible, or fraudulent. The mechanism depends entirely on the issuer's ability to redeem at par. If the bank holding the dollars collapses, if regulators freeze the accounts, or if the reserves were never there to begin with, the peg breaks. The BUSD shutdown in 2023 following regulatory action by the New York Department of Financial Services showed that even well-reserved stablecoins are vulnerable to state intervention.

## Crypto-Collateralized Stablecoins: Overcollateralized Debt

![Algorithmic stablecoin death spiral showing reflexive confidence collapse and token dilution](https://cdn.getmidnight.com/13448471d89a9cd8d7f71026a0334ec8/2026/09/stablecoin-peg-mechanisms-explained-after-h2-3.webp)

Crypto-collateralized stablecoins are backed by onchain digital assets such as ETH, WBTC, or other tokens. Because the collateral itself is volatile, these designs rely on overcollateralization. MakerDAO's DAI requires users to deposit at least $150 worth of ETH to mint $100 worth of DAI. Liquity's LUSD allows a minimum collateralization ratio of 110%, but that lower threshold means liquidations trigger faster during price drops.

The peg is maintained through two mechanisms. First, liquidation: if your collateral falls below the required ratio, the smart contract automatically sells your assets to pay back the stablecoin you minted, plus a penalty. For DAI, that penalty is currently 13%, and the stability fee (interest charged on minted DAI) sits at 8.5% per year. Second, MakerDAO operates a Peg Stability Module that allows users to swap USDC for DAI at a 1:1 ratio with no slippage, capping deviations within a tight band.

DAI also adjusts supply dynamically through the DAI Savings Rate, which rewards holders for locking DAI and the stability fee, which changes the cost of borrowing. When DAI trades above $1, the protocol lowers the cost of minting to increase supply. When DAI trades below $1, the protocol raises the savings rate to increase demand for holding.

The mechanism broke partially in March 2020, when ETH dropped 30% in a single day. A cascade of liquidations overwhelmed the system. Some vaults were liquidated at zero collateral value due to network congestion and oracle delays, leaving MakerDAO with $4 million in bad debt. The protocol survived because governance intervened and recapitalized through a debt auction, but the event showed that extreme volatility can outpace liquidation infrastructure.

Crypto-collateralized stablecoins are vulnerable to oracle manipulation, smart contract bugs, and liquidation cascades during flash crashes. The [CDP mechanism](https://docs.makerdao.com/build/dai.js/single-collateral-dai/collateralized-debt-position) works when collateral prices fall gradually and liquidators have time to act. It fails when prices gap down faster than the protocol can respond. The May 2022 Terra crisis tested this model again. While UST collapsed entirely, [DAI held its peg](https://altcoininvestor.com/passive-income-stablecoins/) with only minor deviations, demonstrating that overcollateralized designs are more resilient to reflexive selling than algorithmic models.

## Algorithmic Stablecoins: The Reflexive Failure Mode

Algorithmic stablecoins try to maintain a peg without holding equivalent reserves. Terra's UST was the largest example. UST was redeemable for $1 worth of LUNA at any time. If UST traded below $1, arbitrageurs were supposed to burn UST and mint LUNA at a profit, contracting UST supply until the peg returned. If UST traded above $1, arbitrageurs would mint UST by burning LUNA, expanding supply until the price fell back to $1.

The mechanism depends entirely on confidence. As long as LUNA has value and users believe UST will return to $1, arbitrage works. But the design is reflexive. When UST falls, the protocol mints new LUNA to defend the peg. That LUNA dilutes existing holders, pushing the price down. As LUNA falls, the credibility of the $1 redemption weakens, which causes more UST selling, which mints more LUNA, which collapses the price further.

In May 2022, large withdrawals from the Anchor protocol - which was offering 20% interest on UST deposits - triggered the initial depeg. UST dropped below $1\. Arbitrageurs began minting LUNA to take advantage of the mispricing. LUNA's supply exploded from 343 million tokens on May 9 to 6.53 trillion one week later, a 1,908,651% increase. The Luna Foundation Guard burned through its entire Bitcoin reserve, from 80,394 BTC (roughly $3.1 billion) to just 313 BTC in seven days, trying to defend the peg. It was not enough. UST collapsed entirely, erasing over $18 billion in value in three days.

The failure was not a surprise to anyone familiar with currency crises. The European Exchange Rate Mechanism crisis in 1992 followed a similar pattern. The British pound was pegged to the Deutsche Mark. When speculators decided the peg was unsustainable, the Bank of England burned through foreign reserves trying to defend it. The reserves ran out, the peg broke, and the pound depreciated 15% in a single day. Algorithmic stablecoins attempt the same defense without reserves. They print their way out of a confidence crisis, which only accelerates the collapse.

Newer algorithmic models claim to have solved the reflexivity problem. Frax v2 uses a hybrid model combining direct collateralization with algorithmic market operations. Ethena's USDe maintains its peg through delta-neutral basis trades, where short perpetual futures positions hedge long spot exposure. These designs are more sophisticated than Terra's, but they have not been tested through a systemic liquidity crisis. The mechanism works when funding rates are positive and liquidity is deep. The test will come when those conditions reverse.

## What Actually Breaks a Peg

Six major depeg events have occurred since 2020, destroying over $45 billion in value. The triggers vary, but the failure modes fall into three categories: reserve depletion, liquidation cascades, and reflexive confidence collapse.

Reserve depletion happens when fiat-backed stablecoins cannot meet redemptions. This can occur because reserves were never adequate, because they are inaccessible (frozen by a regulator or trapped in a failed bank), or because a sudden surge in redemptions overwhelms the issuer's liquidity. The USDC depeg in March 2023 was a liquidity crisis, not a solvency crisis - Circle had the reserves, but a portion was temporarily inaccessible.

Liquidation cascades happen when crypto-collateralized stablecoins face extreme volatility. If ETH drops 30% in an hour, automated liquidations trigger across every CDP. The selling pressure from liquidations pushes ETH lower, triggering more liquidations. If network congestion delays liquidation transactions, some positions become undercollateralized before they can be closed, leaving the protocol with bad debt. March 2020 showed that the mechanism can fail when volatility exceeds the system's ability to liquidate in real time.

Reflexive confidence collapse is the algorithmic failure mode. When holders lose confidence that the peg will hold, they sell. That selling triggers the very mechanism (token issuance) that destroys confidence further. The exit window shrinks as more users realize the design is breaking. Terra's collapse took 72 hours from initial depeg to total failure. There was no recovery because the mechanism itself was the problem.

Cross-chain fragmentation is an additional risk that emerged in 2023-2024\. The same stablecoin - USDC, for example - trades at different prices on different chains if liquidity becomes segmented during a crisis. A holder on Arbitrum might see USDC at $0.98 while Ethereum mainnet shows $1.01, with no easy way to arbitrage the spread if bridging liquidity dries up.

## The Takeaway: No Peg Is Automatic

A stablecoin holds its peg through credible redemption, not code. Fiat-backed stablecoins depend on reserve quality and access. Crypto-collateralized stablecoins depend on overcollateralization and liquidation speed. Algorithmic stablecoins depend on confidence, which is the least stable foundation of all.

The lesson from European monetary history is that pegs are behavioral equilibria, not physical laws. The euro crisis showed that even sovereign debt from developed economies can lose credibility when markets decide the promise is no longer sound. Stablecoins operate under the same constraints. When the mechanism backing the peg is tested - by a bank failure, by a flash crash, by a confidence shock - you discover whether the design was ever credible. Terra failed because its mechanism was reflexive. DAI survived March 2020 because overcollateralization provided a buffer. USDC survived March 2023 because government intervention restored access to reserves.

If you hold stablecoins to [earn yield or move value](https://chain.link/education-hub/stablecoins) across borders, the mechanism matters more than the brand. The yield paid on Anchor's 20% UST deposits was never sustainable because it was subsidized by LUNA issuance, which only worked as long as LUNA retained value. When the confidence loop broke, the yield disappeared with the principal. Real yield comes from fees, spread, or protocol revenue. Subsidized yield comes from new deposits or token emissions, which stop the moment growth reverses.

Since 2022, the market has consolidated around fiat-backed stablecoins for a reason. They are simpler, more transparent, and less vulnerable to reflexive failure. Algorithmic stablecoins now represent only 6-8% of the market by supply as of April 2026, down from over 15% before Terra's collapse. The mechanism that failed once can fail again. The peg is not automatic. It is maintained by reserves, by arbitrage, and by confidence. When any of those breaks, the peg breaks with it.

## Frequently Asked Questions

### What keeps a stablecoin pegged to one dollar?

Three mechanisms maintain stablecoin pegs. Fiat-backed stablecoins like USDC hold bank deposits or Treasury bills and allow authorized participants to redeem tokens for dollars at par. Crypto-collateralized stablecoins like DAI require users to deposit more collateral than the stablecoin value they mint, with smart contracts liquidating positions if collateral falls below thresholds. Algorithmic stablecoins like Terra's UST relied on arbitrage between the stablecoin and a volatile token, expanding or contracting supply to maintain the peg without holding reserves.

### Why did Terra's UST stablecoin collapse in May 2022?

UST collapsed because its peg mechanism was reflexive. When large withdrawals from Anchor caused UST to drop below one dollar, the protocol minted new LUNA tokens to defend the peg. That diluted LUNA holders and pushed LUNA's price down. As LUNA fell, confidence in the one dollar redemption weakened, triggering more UST selling and more LUNA minting. LUNA's supply exploded from 343 million to 6.53 trillion tokens in one week. The Luna Foundation Guard burned through 80,000 BTC trying to defend the peg. The mechanism failed completely within 72 hours, erasing $18 billion.

### What caused USDC to temporarily depeg in March 2023?

USDC fell to 87 cents when Silicon Valley Bank collapsed and Circle disclosed that $3.3 billion of USDC reserves were held at SVB. Holders rushed to exit before Circle could confirm whether those deposits were recoverable. The peg returned within 48 hours after the US government announced it would backstop all SVB deposits, restoring access to Circle's reserves. The depeg was a liquidity crisis, not a solvency crisis. Circle had adequate reserves, but a portion was temporarily inaccessible due to bank failure.

### How does MakerDAO's DAI maintain its peg?

DAI maintains its peg through overcollateralization and two adjustment mechanisms. Users must deposit at least 150% of the DAI value they want to mint in ETH or other collateral. If collateral falls below that ratio, smart contracts automatically liquidate the position with a 13% penalty. MakerDAO also operates a Peg Stability Module that allows one-to-one swaps between USDC and DAI with no slippage, capping deviations. The protocol adjusts the DAI Savings Rate to incentivize holding and the stability fee to change borrowing costs, dynamically managing supply and demand.

### Are algorithmic stablecoins still used after Terra collapsed?

Algorithmic stablecoins represent only 6-8% of the stablecoin market by supply as of April 2026, down from over 15% before Terra's collapse. Newer designs like Frax v2 use hybrid models combining collateral with algorithmic operations, while Ethena's USDe maintains its peg through delta-neutral basis trades. These are more sophisticated than Terra's reflexive design, but they have not been tested through a systemic liquidity crisis. The market has consolidated around fiat-backed stablecoins because they are simpler, more transparent, and less vulnerable to confidence collapse.