Browse our forex tab for a while and a puzzle appears. Most exchange rates wiggle constantly — yet a few, like the UAE dirham, Saudi riyal and Hong Kong dollar, sit at almost exactly the same number year after year. Their charts are ruler-flat. These are pegged currencies, and the machinery holding them still is one of the more interesting corners of global finance.
What a peg is
A currency peg is a public promise by a central bank: our currency will exchange at a fixed rate against another currency, usually the US dollar. The dirham has been fixed near 3.67 per dollar since the 1990s; the Saudi riyal near 3.75; the Hong Kong dollar inside a narrow band around 7.8. The rate does not move because the authority stands ready to buy or sell unlimited amounts at that price.
How the promise is kept
A peg is defended with reserves. If market demand pushes the currency below its peg, the central bank sells dollars from its reserves and buys its own currency until the price returns. If demand pushes it above, it does the opposite — printing local currency to buy dollars, which also builds reserves. A credible peg therefore requires a large war chest of foreign currency and the willingness to mirror the anchor country's interest rates, since any rate gap invites speculators to exploit it.
Why countries choose pegs
Oil exporters like the Gulf states sell their main product in dollars, so a dollar peg makes national income predictable and imports stably priced. Trade hubs value the certainty a fixed rate gives businesses. And for countries with a history of inflation, borrowing the credibility of the dollar can anchor prices at home. The cost is sovereignty: a pegged country largely imports American monetary policy, fitting or not.
When pegs break
Pegs fail when defending them becomes unbearable — reserves run low, or the required interest rates strangle the economy. Speculators sense weakness and attack, selling the currency in size and forcing the bank to burn reserves faster. History's famous breaks, from the pound's 1992 exit from Europe's exchange system to various emerging-market collapses, share a pattern: years of stillness, then a single violent move. A flat chart, in other words, is not the same as a safe one.
Spotting them on the tracker
On our forex tab, compare USD/AED or USD/SAR with a floating pair like USD/TRY. The contrast — one line frozen, one line alive — is the whole lesson in a glance: exchange rates are only as still as someone is willing and able to hold them.