Nominal vs real prices: adjusting for inflation

Published 2026-09-05; updated 2026-09-05.

A nominal price is the number that was quoted at the time, in the money of that moment; a real price restates it in the purchasing power of a single base year by dividing by a price index. The distinction decides which prices count as records. Cocoa’s highest monthly average in cash terms is $10.75 per kilogram, set in January 2025, but in 2024 dollars the peak belongs to July 1977, at about $22.50 per kilogram (World Bank Pink Sheet; BLS CPI via FRED).

Why does adjusting for inflation change the record holder?

Because a dollar is not a fixed unit. It is a claim on goods and services whose size shrinks as the general price level rises, so a price recorded in 1974 dollars and a price recorded in 2026 dollars are measurements in different units. Comparing them without conversion is like comparing a distance in miles with one in kilometers because both are numbers.

The conversion uses a deflator: an index of the general price level, applied by multiplying each historical price by the ratio of the base year’s index to that period’s index. On this site the deflator is the US consumer price index for all urban consumers, published by the Bureau of Labor Statistics and retrieved through FRED, with the average of 2024 as the base. The choice matters. Deflating by consumer prices answers the question “what could this money have bought in an American shop?” Deflating by a manufactures unit value index, as the World Bank does in its own annual real series, answers a different and often more useful question for an exporting country: “how many manufactured imports could this crop have paid for?” The two indexes do not move identically, so the same series can have two defensible real levels.

The base year is less consequential than it looks. Restating a series in 2024 dollars instead of 2010 dollars multiplies every real observation by the same constant, which changes all the numbers and none of the rankings. What the base year does change is legibility, which is why a recent base is worth keeping close to the present.

Two conclusions follow, and both are visible in almost any long commodity series. First, nominal records cluster near the present by construction, so a headline that a price has never been higher is a statement about the currency at least as much as about the commodity. Second, real commodity prices show long waves rather than a trend: the mid-1970s peak that dominates the real records of sugar, coffee, cocoa, wheat and copper alike reflects a period of general inflation combined with genuine shortages, and it is the reference point for the term supercycle.

There is a limit to what the adjustment tells you. A real price is not affordability. Incomes have risen in most countries over the same decades, so a commodity can cost more in constant dollars while taking a smaller share of a household’s spending. And the consumer basket the index measures changes over fifty years, which is a known and unavoidable weakness in any long deflation.

Every one of these commodities set its real record before 2010, and four of the six set it in the 1970s.

A worked example

Cocoa makes the arithmetic visible in three numbers. In July 1977 the World Bank benchmark averaged $4.36 per kilogram. Restated in 2024 dollars using the US consumer price index, that is about $22.50 per kilogram, a multiplier of roughly 5.2 for the intervening 47 years of inflation. In January 2025 the same benchmark averaged $10.75 per kilogram, its highest nominal reading in a series that begins in 1960 (World Bank Pink Sheet; BLS CPI via FRED).

So the 2024 and 2025 spike, which was genuinely the most expensive cocoa in cash terms that anyone trading it had seen, arrived at about 48% of the real 1977 level. Both statements are true at once, and they answer different questions. A chocolate manufacturer budgeting in dollars cares about the nominal number, because that is what leaves the bank account. An economist asking whether cocoa has ever been scarcer relative to everything else cares about the real one. By August 2026 the benchmark was $5.95 per kilogram (World Bank Pink Sheet), which is roughly a quarter of the 1977 real peak.

Sugar shows the pure effect of the deflator, because its nominal and real records fall in the same month. World raw sugar averaged $1.24 per kilogram in November 1974, which is about $7.55 per kilogram in 2024 dollars (World Bank Pink Sheet; BLS CPI via FRED). Nothing about the ranking changes; only the unit does, and the multiple of 6.1 is simply how much the dollar shrank between 1974 and 2024.

Copper shows the case where the two records are closest. Its nominal record is recent, $14,326 per tonne in August 2026, while its real record is April 1974 at about $19,774 per tonne in 2024 dollars, a multiple of 1.4 (World Bank Pink Sheet; BLS CPI via FRED). A metal in the middle of a demand shift has come nearer to its historical real peak than the tropical crops have, which is a more informative comparison than any nominal chart of the same series.

The practical habit is simple: when a price is described as an all-time high, ask in which dollars, and check whether the series is long enough to contain the 1970s. The site’s price pages carry both views, including the cocoa price page, the coffee price page and the copper price page. The 2024 episode itself is covered in the 2024 cocoa spike, the long waves in commodity supercycles, and the source table’s own conventions in how to read the Pink Sheet.

Cite as: Commodity Origins, "Nominal vs real prices: adjusting for inflation", https://commodityorigins.com/learn/nominal-vs-real-prices/ (CC BY 4.0).