Trade-Weighted Exchange Rate

A trade-weighted exchange rate, also called a nominal effective exchange rate (NEER), is an index that measures the value of a currency against a basket of other currencies, each weighted by its share in the country's foreign trade. Instead of asking how the dollar or the rupee has moved against one partner, it asks how the currency has moved against all the countries it actually trades with. Central banks, statistics offices and the BIS publish such indices daily or monthly.

The nominal index uses market exchange rates only. When it is adjusted for differences in price levels or costs, it becomes the real effective exchange rate, the main gauge of price competitiveness. Both are used in monetary policy, because a broad rise in the currency lowers import prices and dampens inflation.

Think of a shopper who buys most of her groceries at one supermarket, some at a second and a little at a corner shop. If prices jump at the corner shop but stay flat at the big supermarket, her overall bill barely moves. To know how her costs really changed, she weights each shop by how much she spends there.

A trade-weighted exchange rate does the same for a currency. If the pound falls sharply against a currency the UK rarely trades with but holds steady against the euro, the index barely moves, because the euro area is a far bigger trading partner. One headline exchange rate, such as against the US dollar, can therefore give a misleading picture.

Most compilers use a geometric weighted average of bilateral exchange rates. A common chain form is:

• $I_t$ is the index value at time $t$, set to 100 in a chosen base period.
• $e_{j,t}$ is the price of the home currency in units of partner currency $j$, so a rise means the home currency has strengthened.
• $w_j$ is partner $j$'s trade weight; the weights add up to 1.
• $\prod$ means multiply the terms for all $N$ partners together.

Worked example: a country has two partners, A with weight 0.6 and B with weight 0.4. Over a month, the home currency rises 5% against A's currency and falls 10% against B's. The index changes by a factor of $1.05^{0.6} \times 0.90^{0.4} \approx 1.0297 \times 0.9587 \approx 0.987$. If the index started at 100, it ends near 98.7: overall, the currency weakened by about 1.3% despite rising against its largest partner.

Weights usually combine imports and exports. Many compilers, including the ECB and the BIS, use "double export weights" that also count competition in third markets: two countries that sell similar goods to the same buyers compete even if they trade little with each other. Weights are updated periodically to reflect changing trade patterns, such as the rise of China.

• The Federal Reserve's nominal broad dollar index. It covers 26 currencies, including the euro as one, weighted by US trade in goods and services, with January 2006 set to 100. It replaced earlier Fed dollar indices in 2019.
• The US Dollar Index (DXY). A widely quoted market index of the US dollar against six currencies, with the euro making up more than half of the weight. Its weights date from 1973 and do not track modern trade, so it is not a true trade-weighted index of current trade.
• The Bank of England's sterling effective exchange rate index. It is published daily and used in Monetary Policy Committee analysis of the pound.
• The ECB's euro effective exchange rates. They are computed against narrow and broad groups of trading partners, in nominal and real terms, for the euro.
• BIS effective exchange rates. Comparable nominal and real indices for around 60 economies, useful for cross-country comparisons.

Trade-weighted rates are used to judge whether a currency is broadly strong or weak, to estimate the pass-through of currency moves into import prices, and in debates about devaluation and competitiveness. Some central banks use them as policy anchors: the Monetary Authority of Singapore runs monetary policy by managing the Singapore dollar's NEER within an undisclosed band. Pegs to a currency basket work in a similar way.

The indices have limits. Trade weights ignore financial links, so a currency's weight in trade may differ from its weight in debt, invoicing or capital flows; much trade is invoiced in dollars whatever the partner. Weights lag behind shifts in trade. Nominal indices can rise simply because a country has lower inflation than its partners, which says little about competitiveness, which is why analysts often prefer the real version. Comparisons with purchasing power parity or the Big Mac index give a different, level-based view of whether a currency is over- or undervalued, while the terms of trade track export versus import prices directly.

• Federal Reserve: H.10 Foreign Exchange Rates and dollar indexes
• BIS: Effective exchange rate statistics