Use the market exchange rate when you are physically moving money across a border — sending remittances, servicing a mortgage in another currency, or saving toward a return home. Use purchasing power parity when you are asking what a salary buys where it is earned. The two can differ by fifty percent or more for the same pair of countries, and choosing between them is not a technicality: it decides whether an offer reads as an increase or a reduction.
The same offer, two different answers
Somebody offers you a job in Warsaw. You convert the salary at the rate your banking app shows and the figure looks modest against what you earn now. A friend who lives there tells you it is a genuinely good salary and that you would live better on it than you currently do. Neither of you is wrong, and neither of you is talking about the same thing.
The market exchange rate tells you what your salary is worth if you take it out of the country. Purchasing power tells you what it is worth if you spend it where you earned it. Those are two separate questions and the answers routinely diverge by a wide margin, particularly between high-income and middle-income economies. The mistake is not using the wrong rate; the mistake is not noticing that a choice was being made at all.
Why they come apart
Exchange rates are set by trade, capital flows and monetary policy, and they respond to things that have nothing to do with the price of a haircut. A great deal of what you actually spend money on — rent, transport, childcare, restaurants, medical appointments — cannot be traded across borders, so its price is set locally and never has to converge with anywhere else.
The result is that in a country with lower local costs, the market rate systematically undervalues what a local salary buys, sometimes dramatically. Move in the other direction and the effect reverses: a salary in an expensive economy converts into an impressive-looking number that buys considerably less than the number suggests. Both errors are large, both are predictable in direction, and both are invisible if you only ever look at one figure.
Which one your question needs
Ask what you are actually going to do with the money, because that is what decides it. If a substantial share of your income has to leave the country — you are supporting family elsewhere, paying down a loan denominated in another currency, or saving in the expectation of returning — then the market rate is the honest one, because that is the rate you will genuinely face.
If you are going to live where you work, spend where you live, and think of the job as your life for the next several years, purchasing power is the measure that answers your question. Most people moving for a job are in the second situation and instinctively use the first tool, because it is the one their phone offers them.
And if you are in both situations at once, which is extremely common, split it. Work out roughly what proportion of your income leaves the country, convert that share at the market rate, and treat the rest as local spending. It is a rough calculation and it is far better than picking one rate and applying it to everything.
Where to find the purchasing power figure
Purchasing power parity conversion factors are published by international statistical bodies for most countries, and comparable domestic indexes exist within countries too — in the United States, regional price parities are published for every metropolitan area. Both are free, both are updated on a schedule, and neither takes more than a few minutes to find once you know the name of the thing you are looking for.
Be wary of any ratio you find quoted inside an article rather than taken from the source. These factors get revised, sometimes substantially, and a number that was accurate when somebody typed it into a blog post quietly stops being accurate without anything announcing the change. The instrument is what you want, not somebody’s snapshot of it. Look up the current factor for the specific pair of countries you care about, note which year it refers to, and write that year down next to the figure so that when you come back to your own notes in three months you know whether they still hold.
Where purchasing power misleads too
It would be convenient if the second rate were simply the correct one, and it is not. A parity factor is built from a basket of goods representing average national consumption, and you are not average. If your spending is unusually concentrated in the things that are locally expensive — housing in the capital city rather than the national average, imported goods, international schooling, travel home — then the national parity figure flatters your situation considerably.
Housing is the biggest single distortion, because it is the largest item in most budgets and it varies enormously within a country. A parity factor computed across a whole nation will not tell you anything reliable about a specific neighborhood in a specific city, which is exactly the level at which you will be making your decision. Use the parity factor for the shape of the answer, then check housing separately at a real address.
A worked version
Suppose an offer converts to $60,000 at the market rate against your current $85,000, and the parity factor says local prices are about two-thirds of what you are used to. On the market rate you are taking a $25,000 cut. On purchasing power the offer is worth something closer to $90,000 of your current spending power, and it becomes a modest raise.
Now suppose a quarter of your income has to go home each month. That quarter converts at the market rate and buys what it buys there. The other three quarters live locally at local prices. Doing it that way gives you a genuinely useful figure and, more importantly, tells you what would have to change for the answer to flip — which is usually the thing you actually want to know.
The practical rule
Convert at purchasing power to decide whether to take the job, and at the market rate to decide what you can send home or save. Say out loud which one you are using whenever you quote a number to somebody else, because half the arguments about international salaries are two people using different rates and neither of them saying so.
And whichever you use, do it last. Convert only after both sides have been reduced to the same quantity — annualized properly, net of what comes out, and after subtracting whatever each salary still has to buy. A perfect conversion applied to two things that were never comparable produces a precise answer to the wrong question.
Common questions
What is the difference between the two rates?
The market exchange rate tells you what your salary is worth if you take it out of the country. Purchasing power tells you what it buys where you earned it. They routinely differ by fifty percent or more.
Which one should I use?
Purchasing power if you are going to live and spend where you work. The market rate if a substantial share of your income has to leave the country.
What if both apply to me?
Split it. Convert the share that leaves the country at the market rate and treat the rest as local spending. Rough, and far better than applying one rate to everything.
Why do the two rates diverge?
Exchange rates respond to trade and capital flows. Rent, transport, childcare and services cannot be traded across borders, so their prices are set locally and never have to converge.
Where do I find a purchasing power figure?
International statistical bodies publish parity conversion factors for most countries, revised periodically. Look up the current one and note the year it refers to rather than relying on a figure someone hardcoded.
When does purchasing power mislead?
When your spending is not average — capital-city housing, imported goods, international schooling, travel home. Housing is the biggest distortion because it varies enormously within a single country.
So is a national parity figure useless?
No, it gives you the shape of the answer. Then check housing separately at a real address, because that is the largest item and the one the national figure smooths away.
When in the process should I convert?
Last. Annualize correctly, subtract what comes out, subtract what each salary still has to buy, and only then convert. A perfect conversion of two incomparable things answers the wrong question precisely.