What actually moves the value of money

Money as a promise, not a thing

Every banknote in your wallet is, technically, worthless paper. What gives it value is collective agreement — that a government will accept it as tax payment, that shops will take it for bread, that the next person will take it from you in turn. Economists call this fiat currency: money whose worth rests on trust and law, not on being backed by gold or silver.

That single idea explains almost everything odd about currency. Because value is agreement rather than substance, it can shift day to day, and the shifting has a name: the exchange rate — how much of one currency it takes to get another.

Why one euro isn't always worth the same dollars

An exchange rate is simply a price — the price of one currency, quoted in another. Like any price, it moves with supply and demand. When more people and institutions want to buy euros with dollars than the reverse, euros become relatively more expensive, and the rate shifts.

What drives that demand is rarely one thing. It's a handful of forces pulling at once, and most currency moves are the net result of several of them acting together.

• Interest rates

  When a country's central bank raises interest rates, savings held in that currency earn more, drawing in foreign money and lifting demand for it.

• Inflation

  A currency losing purchasing power at home tends to lose value abroad too — people trust it less to hold value over time.

• Trade balance

  A country that exports more than it imports sees steady foreign demand for its currency, since buyers need it to pay for those goods.

• Political stability

  Currencies from stable, predictable governments are seen as safer to hold, which supports their value especially in uncertain times.

• Market sentiment

  Traders act on expectations as much as facts — a rate can move on what people believe is about to happen, before it does.

Reading a currency quote

Exchange rates are always written as a pair, because a currency's value only means something relative to another one. A quote like EUR/USD = 1.08 reads as: one euro buys 1.08 US dollars. The first currency listed is the "base"; the second is the "quote" currency you're measuring it against.

A handful of these pairs — dollar against euro, yen, pound, and a few others — account for most of the trading that happens worldwide, simply because those economies do the most trade and hold the most reserves.

A short history of what counts as money

Long before paper notes, communities settled debts by barter — trading a goat for grain, a day's labor for cloth. Barter works only when both sides happen to want what the other has, which is a narrow coincidence to rely on. Coined metal solved that: gold and silver were scarce, durable, and divisible, so they became a middle step anyone would accept.

For most of the twentieth century, paper currencies were still tied to gold — a dollar was, by law, redeemable for a fixed amount of it. That link was formally cut in 1971, when the US moved off the gold standard entirely. Since then, the value of major currencies has floated freely, set by markets rather than by a fixed weight of metal.

The newest chapter is digital: central bank digital currencies and privately issued cryptocurrencies both raise the same old question in a new form — what, exactly, makes something acceptable as money. So far, the answer hasn't changed much: enough people have to agree to treat it that way.

Major currencies at a glance

A small number of currencies dominate global trade and reserves, mostly because of the size and openness of the economies behind them.

Terms worth knowing

Appreciation

A currency becoming more valuable relative to another.

Depreciation

A currency losing value relative to another.

Peg

When a country fixes its currency's value to another, such as the dollar, instead of letting it float.

Reserve currency

A currency held in large quantities by central banks worldwide to settle international trade.

Purchasing power

How much a unit of currency can actually buy, which inflation steadily erodes.

Spread

The small gap between a currency's buying and selling price, which is how exchange services earn a margin.

Central bank

The institution responsible for a country's money supply and interest rates.

Devaluation

A deliberate lowering of a currency's value by the government that issues it.