Why a stablecoin like USDT barely moves

The basic idea: a 1-for-1 promise

A stablecoin like USDT is issued by a company (Tether) that promises one token is worth one dollar. To back the promise, it says it holds reserves against it: cash, short-term US Treasury bills and other assets. In theory, each token issued matches one dollar of reserves.

So the price does not "decide" by itself to stay at $1: it is anchored by what the issuer says it holds.

What keeps it near $1: arbitrage

Suppose USDT drops to $0.997 on an exchange. An operator who can redeem it at $1.00 with the issuer earns the gap: buy 1,000,000 USDT for $997,000, swap them for $1,000,000 and pocket $3,000, or 0.3%. These purchases push the price back up until the gap closes.

The other way round, if it climbs to $1.003, it pays to create new tokens against dollars and sell them. The gap is corrected continuously, often within minutes, by players with no loyalty to the token: they just want the gain.

Why it still moves a little

You will see quotes at 0.9990 or 1.0010. Those wobbles come from the spread (bid-ask gap), momentary liquidity and fees. Direct redemption at $1 is reserved for large clients, with fees and delays; an ordinary saver goes through an exchange and its market price. The more trading there is, the narrower the gap.

When the promise breaks

Stable does not mean risk-free. Two useful examples:

• March 2023, USDC. With part of its reserves stuck in a troubled bank, the token briefly fell to about $0.88 before returning to $1 once access to the funds was secured.
• May 2022, TerraUSD. This so-called "algorithmic" stablecoin had no equivalent reserves: it relied on a sister token. When confidence vanished, it collapsed and dragged that token down with it.

The lesson: stability comes from the quality and availability of reserves and from trust in the issuer. A cash-backed stablecoin does not carry the same risk as an "algorithmic" one.

What it is used for, concretely

Traders use it as a "waiting room": to step out of a volatile asset without going back through a bank, and as a unit of account to compare prices. In a market reading, stablecoin inflows or outflows to exchanges are sometimes followed, but that is context, not a signal.

What to remember

USDT barely moves because its stated reserves and fast arbitrage pull its price toward $1. It can drift away if trust or access to reserves is in question. Checking the issuer, the reserve mix and the published reports is a good habit.