Fundamental analysis · Advanced

Purchasing Power Parity and Currency Valuation

A currency 20% below purchasing power parity is, on average, still 10% below it three to five years later. That is the whole problem with trading it.

Last reviewed 15 September 2026 by the MarketPro research desk · Editorial policy

In short

Purchasing power parity estimates a currency's fair value on the principle that identical goods should cost the same across countries once exchange rates are applied. Absolute PPP compares price levels directly; relative PPP predicts that the higher-inflation currency depreciates by roughly the inflation difference. Deviations from PPP have a half-life of three to five years, which makes it a long-run anchor rather than a trading signal.

What to remember

PPP deviations decay with a half-life of three to five years. A 20% gap today is typically still a 10% gap years later.
Relative PPP, which predicts depreciation equal to the inflation differential, holds far better than the absolute version.
Poorer countries are permanently cheap on PPP, because services cannot be imported and lower wages hold the price level down.
A currency that is both high-yielding and expensive on PPP carries two risks that tend to unwind at the same time.

Lesson 21 of 24 in Fundamental analysis

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Purchasing power parity says that identical goods should cost the same everywhere once you convert currencies. If they do not, the exchange rate is away from the level that would equalise them, and PPP calls that difference over- or under-valuation. It is a long-horizon anchor, and treating it as a trading signal is where people get hurt.

A $5.69 item and a £4.29 item

Suppose a standardised product sells for $5.69 in the United States and £4.29 in the United Kingdom. Divide one by the other and the implied exchange rate is 5.69 divided by 4.29, which is 1.326 dollars per pound.

If the market rate is 1.270, sterling is trading about 4.2% below the rate that would make the item cost the same in both places. On this measure, sterling is undervalued.

Now notice everything this calculation ignores. The item includes local rent, local wages, local tax and local regulation, none of which are traded across borders and none of which arbitrage away. A basket built from a single non-tradable-heavy product measures the cost of labour and property as much as it measures the currency. That is why the single-item version is a teaching device rather than a valuation.

Broader PPP estimates published by international institutions use baskets of hundreds of items and are considerably more careful. They still show developed currencies diverging from PPP by 20% or more for years at a time.

Relative PPP is the version that survives contact with data

Absolute PPP compares price levels. Relative PPP makes a weaker and more defensible claim: the currency of a country with higher inflation should depreciate against one with lower inflation, at roughly the difference in inflation rates.

The arithmetic is direct. Country A runs 5% inflation, country B runs 2%. The expected annual depreciation of A's currency is 1.05 divided by 1.02, which is 1.0294, so about 2.9% a year. Over five years that compounds to roughly 15.6%.

Over long horizons and across countries with large inflation differences, this holds reasonably well. A country running 30% inflation against one running 2% does see its currency fall, and roughly by the amount the differential implies. Between two developed economies with a one point inflation gap, the signal is swamped by capital flows for years at a time.

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Half-lives: why undervalued lasts four years

The empirical literature on PPP converges on an uncomfortable finding. Deviations from PPP do decay, but slowly: the commonly cited half-life is three to five years. That means a currency 20% below PPP today is, on average, about 10% below it three to five years from now.

Put that into a trading context. A 20% valuation gap at 10:1 leverage is a 200% move if it fully closes, which sounds extraordinary until you attach the timescale. Waiting three to five years for half of it, while carrying overnight financing costs and while the gap is free to widen to 30% in the meantime, is not a strategy that survives a margin call. The leverage calculator makes the interim risk concrete in a way that the valuation number never does.

Why poorer countries are structurally cheap

PPP deviations are not random noise waiting to correct. One well-documented effect, named after Balassa and Samuelson, explains a large and permanent part of them: productivity differences in traded goods are much larger between rich and poor countries than productivity differences in services.

A haircut, a taxi ride and a restaurant meal cannot be imported. In a lower-productivity economy, wages in those sectors are lower, so the general price level is lower, so the currency looks undervalued on a basket that includes them. The gap does not close because nothing arbitrages it. It narrows only as the country becomes richer.

The practical consequence is that a permanently cheap currency on PPP is normal for a developing economy, and a valuation model that flags it as undervalued every year for two decades is not producing a signal.

Where PPP still earns its place

As a boundary. A currency 40% from PPP is in unusual territory, which is worth knowing even if it says nothing about timing.
As a check on a carry position. A high-yielding currency that is also expensive on PPP carries two risks at once, and they tend to unwind together.
For high-inflation comparisons. Relative PPP is genuinely useful where inflation differentials are large, which is most of the emerging market universe.
As a corrective to extrapolation. It is a reminder that a multi-year trend has a level it is moving away from.

Use it as context alongside the drivers that actually move a rate week to week, principally the interest rate differential. PPP tells you where a currency sits relative to a long-run anchor. It does not tell you what happens next quarter, and it has never claimed to.

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Written and reviewed by the MarketPro research desk

MarketPro is a trading-signal and trading-education app operated by Harajuku Holdings LTD (Cyprus). Our signal desk publishes and tracks every trade idea in-app, and every page here is checked against the app's live behaviour before publishing. Last reviewed 15 September 2026. How we produce signals and content · About MarketPro

FAQ

Purchasing Power Parity and Currency Valuation: questions

Can purchasing power parity be used to trade currencies?

Not directly, because it has no timing component. Deviations from PPP persist for years and can widen substantially before they narrow, with an empirical half-life of three to five years. A leveraged position waiting for that convergence faces financing costs and the real possibility of a margin call long before the valuation gap closes. It is used as context rather than as an entry signal.

Why do exchange rates stay away from PPP for so long?

Because capital flows dwarf trade flows in determining exchange rates over short and medium horizons. Interest rate differentials, investment flows and risk sentiment move far more money than the arbitrage of goods prices. Additionally, a large part of any price basket consists of services, rent and labour that cannot be traded across borders, so no arbitrage mechanism exists to close that portion of the gap.

What is the difference between absolute and relative PPP?

Absolute PPP compares price levels directly and derives an implied exchange rate from the ratio. Relative PPP makes the weaker claim that the change in the exchange rate should match the difference in inflation rates between two countries. Relative PPP performs considerably better empirically, particularly where inflation differentials are large, which is most of the emerging market universe.

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