Introduction
I’m going to use a simple example to explain the difference between two concepts that are often confused: Market Exchange Rates (MER) and Purchasing Power Parity (PPP).
Stop me if you’ve heard this before: I moved to the UK and now I earn £2,000 a month — that’s more than seven times my old ₦500,000 salary as a bank manager in Nigeria.
I moved to the UK and now I earn £2,000 a month — that’s more than seven times my old ₦500,000 salary as a bank manager in Nigeria.
A £2,000 UK salary seems like a jackpot compared to ₦500,000 in Nigeria — until you look at what those numbers actually buy.
On paper, the maths looks straightforward. Convert both incomes into the same currency and the person in the UK appears to have made a dramatic leap forward, while the person in Nigeria seems to be falling behind.
But that conclusion is only half the story — and most times, it’s the wrong one.
To understand why, we need to separate two ideas that are frequently mixed up: Market Exchange Rates (MER) and Purchasing Power Parity (PPP).
The Market Exchange Rate view: income in global money
Let’s start with the most familiar approach.
Assume the market exchange rate is:
£1 = ₦1,800
Now convert both incomes into the same currency.
UK worker: £2,000 × 1,800 = ₦3.6 million
Nigerian worker: ₦500,000
On this basis, the UK worker appears to earn more than seven times as much. This is a market exchange rate comparison, and it answers a specific question:
How much is this income worth in international financial terms?
All else being equal, for an ordinary person living in Nigeria, this comparison only really matters if they are involved in international trade, foreign investment, have dollar-denominated debt, or regularly purchase goods priced on global markets.
For everyday life, however, it tells us very little about how people actually live.
The missing piece: prices are not the same everywhere
People do not consume “exchange rates”. They consume goods and services — rent, food, transport, energy, childcare. And these cost very different amounts in different countries.
So let’s introduce a simple cost-of-living comparison. Assume the same basic monthly basket of goods costs:
£1,200 in the UK
₦300,000 in Nigeria
Now we can calculate a Purchasing Power Parity (PPP) rate:
PPP rate = ₦300,000 ÷ £1,200 = ₦250 per £
This means: ₦250 in Nigeria buys what £1 buys in the UK.
Re-evaluating the incomes using PPP
Now convert the UK salary using the PPP rate instead of the market rate:
UK worker (PPP-adjusted): £2,000 × 250 = ₦500,000 (PPP equivalent)
Compare again:
UK worker (PPP): ₦500,000
Nigerian worker (actual): ₦500,000
Suddenly, the picture changes. From a purchasing power perspective, both workers can afford roughly the same standard of living for that basket of goods (rent, food, utilities etc).
The UK worker earning £2,000 can afford about 1.66 baskets (£2,000 ÷ £1,200), while the Nigerian worker earning ₦500,000 can also afford about 1.66 baskets (₦500,000 ÷ ₦300,000).
An important clarification (often misunderstood)
It is perfectly reasonable to point out that living conditions differ across countries. The UK, for example, benefits from stronger public infrastructure, more developed healthcare systems, and wider social protections.
That observation, however, speaks to the overall quality of life, not to how far your money can carry you in a typical month.
Understanding that distinction helps avoid talking past one another when discussing, especially, wages.
A Final Reality Check: The "iPhone" Factor
Another important point is that while PPP shows us how people live locally, it has a major limitation: not everything is priced locally. Economists split spending into two categories:
Non-Tradable Goods (PPP Wins): Things like rent, haircuts, doctor visits, and local produce. These are cheaper in Nigeria because local labour is cheaper. This is where the ₦500,000 feels like £2,000.
Tradable Goods (Market Rate Wins): Things like smartphones, cars, fuel, and software subscriptions. These are priced on the global market.
The Bottom Line: If both workers want to buy the latest iPhone, the UK worker only needs about half of one month's salary. The Nigerian worker, however, would need to spend nearly three months' salary for the exact same phone.
This is why PPP is the best measure for poverty and welfare, but the Market Exchange Rate is still the king of global purchasing power.
