Current USD vs constant USD vs PPP — which one should you use?

Every income or GDP figure in our database comes in three currencies: current USD, constant USD, and PPP (purchasing power parity). Most clients pick one and move on without asking why there are three — until a number looks wrong, or two analysts on the same project get different answers from the same dataset.

The three aren't interchangeable, and using the wrong one for a given question produces a confidently wrong answer. This piece explains what each one actually measures, when to reach for which, and how to convert any of them into local currency using the exchange rate data we provide alongside.

The three currencies, in one sentence each

Current USD — what something was actually worth, then

Current USD is the nominal value in the dollars of that specific year. No adjustment for inflation, no adjustment for purchasing power — just the dollar figure as it stood at the time. If a city's middle-income threshold was $2,009 in 2024, that's the actual number a household needed to earn that year to sit in that bracket.

This is the right currency when you're working with a single point in time: pricing a contract, sizing a market today, or reporting a budget for the current year. It's the wrong currency the moment you start comparing across years, because a 2024 dollar and a 2010 dollar don't buy the same amount — inflation has eroded the 2010 dollar's purchasing power in between.

Constant USD — real growth, with inflation stripped out

Constant USD answers a different question: how has this value changed in real terms, independent of inflation? We anchor every series to 2015 prices using each country's own GDP deflator. A constant-USD figure for 2024 tells you what that 2024 nominal value is worth in 2015 purchasing power — which is the number you actually want when comparing growth across a decade.

The gap between current and constant USD widens the further you move from 2015. Take Windhoek's high-income threshold: in nominal current USD it's been fixed at $5,478.75 for 2000 through 2024 by definition of the income class boundary. But viewed in constant 2015 USD, that same nominal threshold was worth $14,540 in 2000 (Namibia's currency had far less inflation behind it then) and only $3,520 by 2024 — a near four-fold real decline, entirely explained by 24 years of accumulated inflation eroding what a fixed nominal dollar figure represents in real terms.

Notice the two columns are identical in 2015 — that's not a coincidence, it's the base year, and constant USD always converges to current USD exactly at the anchor point. This is the currency to reach for whenever the question is "has this actually grown" rather than "what is this worth right now."

PPP — what a dollar actually buys, locally

PPP adjusts for the fact that a dollar doesn't buy the same basket of goods in every country. $1,000 goes much further in rural Malawi than it does in central Lagos, even before exchange rates enter the picture — local prices for housing, food and services simply differ. PPP conversion factors (we use ICP 2017 factors via World Bank's PA.NUS.PPP) correct for this, making it the right currency for comparing living standards or market size across countries.

Use PPP when the question is fundamentally cross-country: is the middle class in Kenya bigger in real purchasing terms than in Ghana? Is a $50/month subscription price more or less burdensome in Rwanda than in South Africa? Current or constant USD will mislead you here, because they don't account for how far a dollar actually stretches locally.

Converting to local currency

All three of the above are still USD-denominated. Clients doing market entry analysis or pricing work often need the figure in the local currency unit instead — Nigerian naira, Kenyan shillings, Ghanaian cedi. We provide exchange rate data (PA.NUS.FCRF — official exchange rate, LCU per USD) with historical coverage from 2000 and forecasts through 2035, so any current-USD figure in our database can be converted to local currency by multiplying by the matching year's exchange rate.

The exchange rate forecasts use a dampened trend model calibrated by currency regime: hyperinflation economies (Zimbabwe, Sudan, South Sudan) use a more conservative dampening factor given how structurally unstable those rates are, while CFA franc zone countries and other pegged currencies are forecast with a near-flat trend reflecting their peg to the euro or US dollar. This avoids the common mistake of extrapolating a wildly depreciating currency in a straight line for ten years, or assuming a pegged currency will suddenly start floating.

Worked example

Say you want Nigeria's GDP per capita for 2024 in naira rather than USD. Our database shows current USD GDP per capita, and the PA.NUS.FCRF series gives you that year's official exchange rate. Multiply the two, and you have the local currency figure — no separate currency API or manual lookup required, since both series sit in the same dataset and can be pulled together in a single API call or dashboard download.

Why this matters for due diligence and market entry work

Picking the wrong currency type doesn't just produce a slightly-off number — it can flip the conclusion. A market that looks like it's grown 40% in current USD terms might be flat or even shrinking in constant USD once inflation is accounted for. A country that looks poorer than its neighbour in nominal USD might have a larger real middle class once PPP is applied. Serious analysis depends on knowing which lens the question requires before reaching for a number.