What Is a Stablecoin? How It Maintains Its Peg

The cryptocurrency market moves fast. Bitcoin can swing 10% in a single day. Ethereum can drop 15% in hours. For traders and protocols that need predictable value, this volatility went from feature to bug. Stablecoins emerged as the solution—digital assets designed to maintain a steady value, typically pegged to a traditional currency like the US dollar. But the word “stable” does a lot of heavy lifting, and understanding how these tokens actually preserve their peg requires digging into the mechanics beneath the surface.

This guide covers what stablecoins are, the three primary mechanisms used to maintain their peg, and the risks that come when those mechanisms fail. You’ll find specific examples of major stablecoins, a comparison of how each type works, and a clear-eyed look at what happens when a peg breaks.

What Is a Stablecoin?

A stablecoin is a cryptocurrency designed to minimize price volatility by anchoring its market value to an external reference. The most common reference is the US dollar, though stablecoins pegged to the euro, gold, or even other cryptocurrencies exist. The goal is straightforward: combine the speed, transparency, and programmability of blockchain with the predictable purchasing power of a traditional asset.

Stablecoins serve several functions in the crypto ecosystem. Traders use them as a safe harbor during market turbulence, moving funds out of volatile tokens without exiting the crypto economy entirely. Decentralized finance (DeFi) protocols require stablecoins as collateral for loans and as liquidity for trading pairs. Cross-border payments and remittances benefit from stablecoins’ near-instant settlement and lower fees compared to traditional wire transfers.

Not all stablecoins achieve their stability goals equally. Some maintain their peg through full reserves of fiat currency held in bank accounts. Others use cryptocurrency collateral with over-collateralization to absorb price swings. A third category—algorithmic stablecoins—attempts to maintain pegs through smart contracts and monetary policy without tangible reserves. Each approach carries distinct trade-offs in terms of decentralization, transparency, and risk.

How Do Stablecoins Maintain Their Peg?

The peg mechanism is the core differentiator among stablecoin designs. Put simply, the peg is the promise that one unit of the stablecoin equals one unit of the underlying asset—usually $1. How that promise gets kept varies significantly across different architectures, and the method chosen determines the stablecoin’s resilience under market stress.

When demand for a stablecoin rises, the issuing mechanism must expand supply. When demand falls, supply must contract. The challenge is doing this in a way that maintains the $1 anchor without requiring constant manual intervention. The three primary mechanisms each solve this problem differently.

Fiat-Collateralized Stablecoins

Fiat-collateralized stablecoins maintain their peg by holding actual fiat currency reserves equal to or greater than the number of tokens in circulation. For every stablecoin minted, $1 sits in a bank account somewhere. When a user wants to redeem their tokens for fiat, they burn the tokens and the issuer withdraws from reserves.

USDC, issued by Circle, is the dominant example. Circle maintains transparent reserves with monthly attestations from accounting firms, and users can redeem USDC directly through the company for a fee. Tether (USDT) operates similarly but has faced ongoing controversy over whether its reserves truly match its circulating supply. Multiple investigations and settlements with the New York Attorney General have forced Tether to improve its disclosure practices, though critics still question the composition of its reserves.

The advantage of fiat-collateralized stablecoins is simplicity. The peg relies on actual cash sitting in accounts—a straightforward mechanism that works well under normal market conditions. The limitations include centralization (a single issuer controls the supply), counterparty risk (you must trust the issuer to hold the reserves), and the need for banking relationships that can be disrupted.

Crypto-Collateralized Stablecoins

Crypto-collateralized stablecoins maintain their peg using other cryptocurrencies as collateral rather than fiat currency. The key innovation here is over-collateralization—users must deposit more value than they want to borrow. If the collateral’s value drops, the position gets liquidated automatically.

DAI, created by the Maker protocol, is the most established example. To generate DAI, users lock Ethereum (or other accepted collateral) into a smart contract. The system requires a minimum collateral ratio of 150% or higher, meaning $150 worth of ETH backs every 100 DAI created. This buffer absorbs price drops in the underlying collateral while maintaining the $1 peg.

The crypto-collateralized approach offers greater decentralization—no single issuer controls the supply, and the mechanism runs through transparent smart contracts. However, it introduces complexity for users, who must manage collateral ratios and monitor liquidation thresholds. During the Terra collapse in May 2022, similar crypto-collateralized protocols faced severe stress as correlated sell pressure drove collateral values down simultaneously.

Algorithmic Stablecoins

Algorithmic stablecoins attempt to maintain their peg without holding any collateral reserves. Instead, they use algorithms and smart contracts to expand and contract supply based on market conditions. The theory goes: when demand rises and the price exceeds $1, the protocol issues more tokens to bring the price down. When demand falls and the price drops below $1, the protocol reduces supply or offers incentives to burn tokens.

This approach promises full decentralization—no bank accounts, no custodians, no single point of failure. It also promises trouble, as the Terra collapse demonstrated. Terra’s UST used a sister token (LUNA) as a sort of shock absorber for the peg mechanism. When a massive sell-off hit in May 2022, the algorithm couldn’t expand supply fast enough to maintain the peg. Both UST and LUNA collapsed from billions in combined market capitalization to effectively zero within days.

The lesson here is that algorithmic stability requires market confidence as its underlying asset. Without real reserves, the peg rests entirely on the belief that the mechanism will work—and belief evaporates quickly during a crisis. Most algorithmic stablecoin experiments since Terra have either failed or pivoted to hybrid models that incorporate actual collateral.

What Happens If a Stablecoin Loses Its Peg?

A stablecoin losing its peg—often called a “de-peg event”—can happen through bank runs on fiat-backed issuers, over-leveraged positions in crypto-collateralized systems, or the collapse of algorithmic mechanisms during market panic. The consequences vary by mechanism, but the pattern is consistent: when the peg breaks, the market punishes the token severely.

For fiat-collateralized stablecoins, a de-peg typically stems from a loss of confidence in the issuer’s solvency. If users believe the reserves aren’t there, they rush to redeem—creating a bank run that may exceed even real reserves. USDT has experienced several episodes where its price dropped briefly below $1 (as low as $0.95 during the 2022 market crash), each time triggering panic but eventually recovering as confidence returned.

For crypto-collateralized stablecoins, de-peg events often occur during rapid market downturns when collateral values plummet faster than liquidation mechanisms can handle. The cascading liquidations become a feedback loop: collateral sells off, prices drop further, more liquidations trigger. MakerDAO survived this scenario multiple times, but each stress test revealed weaknesses in the system.

For algorithmic stablecoins, the de-peg is usually catastrophic and final. Without reserves to absorb losses, the mechanism has nothing to stop the slide once market confidence breaks. The Terra collapse wiped out approximately $40 billion in combined market value within a week.

Popular Stablecoins and Their Peg Mechanisms

Stablecoin	Mechanism	Collateral	Market Cap (2024)
USDT	Fiat-collateralized	Cash + reserves	~$95 billion
USDC	Fiat-collateralized	Cash + US Treasuries	~$35 billion
DAI	Crypto-collateralized	ETH, other crypto	~$5 billion
TUSD	Fiat-collateralized	Cash + equivalents	~$5 billion
USDD	Algorithmic/hybrid	TRX collateral + reserves	~$750 million

These figures fluctuate significantly based on market conditions and competitive dynamics within the stablecoin market.

Conclusion

Stablecoins are neither as stable as their name suggests nor as risky as their worst failures imply. The mechanism matters enormously. Fiat-collateralized stablecoins like USDC offer reliability but depend on trusted issuers and traditional banking infrastructure. Crypto-collateralized stablecoins like DAI provide decentralization but require active management and carry liquidation risk. Algorithmic stablecoins remain largely experimental after the Terra disaster demonstrated what happens when code meets a market panic.

The stablecoin landscape continues evolving. Regulatory pressure is pushing issuers toward greater transparency and reserve segregation. New models—hybrid systems that combine crypto collateral with partial fiat reserves—aim to capture benefits from multiple approaches. What remains clear is that “stable” is not a property but a promise, and promises only hold when the mechanism behind them is strong enough to survive the next crisis.