How Do Stablecoins Hold Their Peg? Reserves and Arbitrage

A stablecoin is a cryptocurrency designed to track the value of another asset, almost always a fiat currency such as the US dollar, so its price stays close to a fixed target instead of floating freely. Holding that target is called maintaining a peg, and it is not automatic. A peg survives only because specific mechanisms, different for each design, keep pulling the market price back towards it.

What “Holding a Peg” Actually Means

Every stablecoin sits somewhere between two ideas: a promise and a mechanism. The promise is that one unit of the stablecoin can always be treated as equivalent to one unit of the target asset. The mechanism is whatever process makes that promise credible enough for the market to believe it, trade it, and arbitrage it back into line whenever it drifts. Three broad mechanism families exist, fiat-backed, crypto-backed, and algorithmic, and each holds its peg through a different combination of reserves, collateral, and market incentives.

Fiat-Backed Stablecoins and Reserves

The most widely used stablecoins, including Tether and USD Coin, are fiat-backed: the issuer holds reserves, typically a mix of cash and short-term, low-risk instruments, intended to roughly match the number of tokens in circulation. When a large holder redeems tokens directly with the issuer, the issuer is meant to return equivalent value from those reserves and remove the redeemed tokens from supply. The peg holds because that redemption path exists and is trusted; if the market doubts the reserves are sufficient or accessible, the peg can weaken even before any actual redemption is attempted. This is why reserve composition, custody arrangements, and the frequency and quality of independent attestations matter so much for this category. They are the entire basis for trust in the promise.

Crypto-Backed and Overcollateralised Designs

A second family, exemplified by Dai, backs its stablecoin with other cryptocurrencies locked in smart contracts rather than with cash in a bank account. Because crypto collateral is volatile, these systems are typically overcollateralised: a user must lock in more value than the stablecoin they generate, leaving a buffer against price swings. If collateral value falls too close to the value of the stablecoin issued against it, the position can be automatically liquidated to protect the system. This design trades counterparty risk, trusting an issuer’s bank reserves, for a different set of risks: smart-contract risk, collateral volatility, and liquidation mechanics that must function correctly under stress, including during periods when the wider market is falling quickly and liquidations cluster together.

The Role of Arbitrage

Reserves and collateral explain why a peg can hold; arbitrage explains why it usually snaps back quickly after drifting. If a stablecoin trades slightly above its target, traders with direct mint-and-redeem access are incentivised to create new tokens at the peg price and sell them into the market at the higher price, pushing it back down. If it trades slightly below target, the same traders can buy the cheaper tokens on the open market and redeem them at full value, pushing demand, and the price, back up. This constant, profit-driven correction is what keeps well-designed stablecoins trading within a narrow band around their target most of the time, without any central authority actively managing the price tick by tick.

Direct mint-and-redeem access is usually reserved for large, verified counterparties working directly with the issuer, rather than offered to every individual holder. Most people interact with a stablecoin purely on the secondary market, buying and selling on an exchange rather than minting or redeeming with the issuer at all. The peg still benefits from this arrangement, because the smaller set of participants who can arbitrage directly keep pushing the secondary market price back towards target on everyone else’s behalf. When that direct access narrows, for instance if an issuer restricts redemptions to a smaller group or introduces delays, the arbitrage loop that normally keeps the price anchored can weaken even if reserves themselves remain intact.

When Pegs Break

A depeg happens when the market loses confidence in the mechanism faster than arbitrage or redemptions can restore it. For fiat-backed coins, that usually starts with doubts about reserve quality, access, or custody. For crypto-backed coins, a sharp and fast fall in collateral value can overwhelm the liquidation system before it can respond, especially if liquidity is thin during the move. Algorithmic designs that rely on a second, unbacked token to absorb demand shocks, rather than on hard reserves or overcollateralisation, have historically proven the most fragile, because the mechanism that is supposed to restore the peg can itself lose value in a self-reinforcing spiral once confidence breaks. None of this means every stablecoin carries equal risk; it means the source of a coin’s stability is worth understanding before treating any stablecoin balance as risk-free.

Stablecoins increasingly exist on more than one blockchain at once, which adds a further layer worth understanding. Moving a stablecoin between networks typically relies on a bridge: infrastructure that locks tokens on the original chain and mints a representative version on the destination chain. A stablecoin can be soundly reserved or well overcollateralised on its home chain while a bridged version on another network carries an additional dependency, since the bridge itself has to keep functioning correctly and remain solvent for the bridged token to keep trading in line with the original. This doesn’t make multi-chain stablecoins inherently riskier in every case, but it is a separate risk layer, distinct from the reserve or collateral question, that’s easy to overlook when checking only the headline peg price.

Reading the Signals Yourself

Because the mechanisms differ so much, a single question, is this stablecoin safe, doesn’t have one answer. More useful questions are specific to the design: for a fiat-backed coin, how transparent and frequent are reserve attestations? For a crypto-backed coin, how has the collateral ratio behaved during past periods of market stress? For any stablecoin, how deep is its trading liquidity, and how has its price actually behaved, tick by tick, during turbulent markets rather than calm ones? Live pricing and peg data, such as the figures tracked on our stablecoins desk, are a more useful starting point than any issuer’s marketing material.

None of this is financial advice, and holding a stablecoin is not risk-free simply because the word stable is in the name. Treat every design on its own mechanical merits and do your own research before relying on one. For a closer look at how the three main designs compare side by side, see our guide to the different types of stablecoins.