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PPP is the closest thing economics has to a 'fair value' of a currency. Here's how it works — and where it falls short.
A simple, powerful idea
Purchasing power parity (PPP) says that, in the long run, the same basket of goods should cost the same amount everywhere — once you convert through the exchange rate. If a haircut costs $30 in New York and €25 in Paris, the "fair" EUR/USD rate would be 30 / 25 = 1.20.
If the actual market rate is 1.10, the euro is undervalued. If it's 1.30, overvalued. The market may move that way over time… or may not.
Why it matters
PPP gives you a way to compare living standards across countries that's more honest than just converting GDP at market rates. A salary of $20,000 in Vietnam buys far more than the same dollars in San Francisco — PPP captures that.
It's also a long-term anchor for currency analysts. Big deviations from PPP often (slowly) close over years.
The Big Mac Index
In 1986, *The Economist* magazine launched the Big Mac Index — a playful but surprisingly insightful way to apply PPP. The Big Mac is sold worldwide, with broadly similar inputs (beef, bread, lettuce, labor, rent), so its price in different countries gives a rough sense of currency mispricing.
If a Big Mac costs $5.50 in the U.S. and 22 yuan in China, the "Big Mac" exchange rate is 22 / 5.50 = 4.0. If the actual USD/CNY rate is 7.2, the yuan is roughly 44% undervalued by this measure.
The index isn't a forecasting tool — it's a teaching tool. But it consistently sparks better conversations about currencies than most professional models.
Why PPP isn't a perfect predictor
- Non-traded goods: services, rent, and labor don't move across borders. A haircut in Manila will always cost less than in Manhattan.
- Tariffs and trade barriers: distort cross-border prices.
- Brand premiums: a Big Mac, an iPhone, or a Starbucks coffee can carry different markups in different markets.
- Quality differences: a "comparable" basket of goods is rarely truly comparable.
- Capital flows: short-term FX moves are dominated by capital flows, not trade — and capital flows ignore PPP.
How professionals use PPP
- The OECD and IMF publish PPP-adjusted GDP figures for international comparisons.
- Long-term currency strategists use deviation from PPP as one of several signals.
- Multinational corporations use PPP for setting expat salaries.
- Travelers and freelancers intuitively use it when deciding where to live, work, or vacation.
When PPP fails most spectacularly
In economies with capital controls, asset bubbles, or sustained policy interventions, market exchange rates can stay disconnected from PPP for years — even decades. China and Switzerland are two long-running examples.
A practical takeaway
You don't need an econometrics degree to use PPP. Just ask:
- "How does the cost of a meal, a coffee, a haircut, and a hotel night compare to home?"
- "Am I getting more or less than I would with the same money at home?"
- "If I'm earning in a strong currency and spending in a weak one, what's my real purchasing power?"
These intuitive comparisons are PPP in action.
Key takeaways
- PPP says the same goods should cost the same everywhere, after FX conversion.
- It's a long-term anchor for currency analysis, not a short-term forecaster.
- The Big Mac Index makes PPP tangible — and surprisingly useful.
- For travelers and remote workers, intuitive PPP awareness changes financial decisions.