Advanced Financial Management · Management of international trade and finance

Exchange Rate Determination and Forecasting for ACCA AFM

Updated 11 October 2026 · Fact-checked

Exchange rate forecasting in AFM uses three parity relationships. Purchasing power parity links spot rates to inflation differences. Interest rate parity links forward rates to interest rate differences. The international Fisher effect links interest rates to inflation. You multiply the base rate by a ratio of (1 + rate) terms.

Understand Exchange Rate Determination and Forecasting

An exchange rate is the price of one currency in terms of another. Over time, rates move because countries have different inflation and interest rates. The three parity theories give a rule for each link. They are models, not guarantees. You use them to forecast and to explain.

Purchasing power parity (PPP) says the same basket of goods should cost the same in both countries once converted. If a country has higher inflation, its currency should weaken by the inflation gap. PPP is about the expected future spot rate. It tends to hold only over the long run, because trade barriers, transport costs and non-traded goods keep prices apart.

Interest rate parity (IRP) says the forward rate reflects the interest rate gap between the two currencies. The currency with the higher interest rate trades at a forward discount. If it did not, you could borrow in one currency, lend in the other, lock in the forward rate and make a risk-free profit. That is arbitrage, so the forward rate is pinned down. IRP gives the forward rate and normally holds closely in open markets.

The Fisher effect says a nominal interest rate is made up of a real rate and expected inflation. The international Fisher effect says the interest rate gap between two countries predicts the expected change in spot rate. It assumes real rates are equal across countries. Combine it with PPP and you get a consistent set: higher inflation means higher interest rates and a weaker currency.

Know the difference. PPP and the international Fisher effect forecast the future spot rate. IRP gives the forward rate. The forward rate is not a forecast of the future spot rate, though the expectations theory says it is an unbiased predictor. Examiners often ask you to compare forecasts and comment on why they differ.

Key rules to remember

Purchasing power parity (future spot rate): S1 = S0 × (1 + hc) ÷ (1 + hb); Rate is quoted as units of the counter currency per 1 unit of the base currency. hc is the inflation rate in the counter currency country. hb is the inflation rate in the base currency country.
Interest rate parity (forward rate): F0 = S0 × (1 + ic) ÷ (1 + ib); Same quoting convention. ic and ib are interest rates for the same period as the forward contract. Adjust for the time period, for example use 6/12 of the annual rate for six months.
International Fisher effect: S1 ÷ S0 = (1 + ic) ÷ (1 + ib); Uses nominal interest rates to forecast the expected future spot rate. Assumes equal real interest rates.
Fisher effect (closed economy): (1 + nominal rate) = (1 + real rate) × (1 + inflation rate); Use it to split a nominal rate into real rate and inflation.
Four-way equivalence link: (1 + ic) ÷ (1 + ib) = (1 + hc) ÷ (1 + hb) = F0 ÷ S0 = E(S1) ÷ S0; This is a theoretical set. In practice the links hold only approximately, and the forward and spot expectations usually differ.

How to solve Exchange Rate Determination and Forecasting questions

Use this method for any question on forecasting rates or explaining currency movements.

1Write down the quote. Identify which currency is the base (the 1 unit) and which is the counter (the units per 1).
2Identify what is asked: a future spot rate (use inflation or the Fisher effect) or a forward rate (use interest rates).
3Pick the correct rates. Inflation rates for PPP. Nominal interest rates for IRP and the international Fisher effect.
4Match the time period. Convert annual rates to the period needed, for example 6/12 of the annual rate for a six-month forward, or compound over several years.
5Put the counter currency country's rate on top and the base currency country's rate on the bottom, then multiply by the starting rate.
6Check direction. The currency with higher inflation or higher interest should weaken, so the rate quoted in its terms should rise.
7Finish the requirement: state the forecast, then comment on reliability, differences between methods, and what it means for the decision or hedge.

Quickest way: Counter over base

When to use it: Use it for any numerical forecast when time is short.

Write: new rate = old rate × (counter rate ÷ base rate).
Use inflation for a future spot, interest for a forward.
Insert (1 + rate) for each country, raised to the number of years if the period is more than one year.
Sense check: the country with the higher rate has the weaker currency, so its units per 1 of the other currency rise.
Show the one line of working and move on to the written comment, which carries many marks.

Common mistakes in Exchange Rate Determination and Forecasting

Putting the ratio upside down
Students forget which currency is base and which is counter.
Fix: Label the quote first. The counter currency is the number you are forecasting, so its country's rate goes on top.
Using inflation rates for a forward rate or interest rates for a PPP spot forecast
The theories look the same, so the inputs get mixed up.
Fix: Remember: inflation gives PPP spot, interest gives IRP forward. The international Fisher effect gives a spot forecast but uses interest rates.
Ignoring the time period
Annual rates are given, but the forward is for three or six months.
Fix: Scale the rate to the period, for example 6/12 of the annual rate, before using the formula, unless the question says to compound.
Saying the forward rate is a forecast of the future spot rate
Both are future rates, so they are treated as the same thing.
Fix: Say the forward rate is set by interest rate differences through arbitrage. It may differ from the actual future spot rate.
Claiming the parity theories always hold
Students learn the formulas without the assumptions.
Fix: State that PPP holds mainly in the long run, IRP holds closely because of arbitrage, and the international Fisher effect needs equal real rates. Name frictions such as capital controls, transaction costs and government intervention.
Giving the calculation with no comment
Students treat it as a pure computation question.
Fix: Add a sentence on the implication, for example what the forecast means for the hedge or the project cash flows, to earn professional skills marks.

Worked examples

Example 1

The spot rate is $1.60 per £1. Expected annual inflation is 2% in the UK and 5% in the US. Using purchasing power parity, forecast the spot rate in three years' time. Comment briefly.

Show the solution

Base currency is £, counter currency is $, so the quote is $ per £1 and S0 = 1.60.
Counter inflation hc = 5% (US). Base inflation hb = 2% (UK).
S3 = 1.60 × (1.05 ÷ 1.02)^3.
1.05 ÷ 1.02 = 1.029412.
1.029412^3: 1.029412² = 1.059689, then × 1.029412 = 1.090858.
S3 = 1.60 × 1.090858 = 1.7454.
The dollar is expected to weaken against the pound because US inflation is higher.

Answer: Forecast spot rate in three years is about $1.745 per £1. The dollar weakens because US inflation is higher. PPP is a long-run guide, so the actual rate may differ.

Example 2

The spot rate is ₹84.00 per $1. The annual interest rate is 7% in India and 3% in the US. Calculate the six-month forward rate using interest rate parity. Explain why the rupee trades at a forward discount.

Show the solution

Base currency is $, counter currency is ₹, so S0 = 84.00 and the quote is ₹ per $1.
Scale the annual rates to six months: India 7% × 6/12 = 3.5%. US 3% × 6/12 = 1.5%.
F0 = 84.00 × (1.035 ÷ 1.015).
1.035 ÷ 1.015 = 1.019704.
F0 = 84.00 × 1.019704 = 85.655.
The rupee needs more units to buy one dollar forward, so it is at a forward discount.
Reason: India has the higher interest rate. If the forward rate did not offset this, arbitrageurs could borrow in the low-rate currency, deposit in the high-rate currency, and lock in a profit using the forward.

Answer: Six-month forward rate is about ₹85.66 per $1. The rupee is at a forward discount because its interest rate is higher, and arbitrage keeps the forward rate in line with the interest rate gap.

Exam tips

Read the quote carefully. Many marks are lost by flipping the ratio. Write the base and counter currency next to your working.
Show each step and state the period used. Method marks are given even if the arithmetic slips.
Always add comment: why the forecast may be wrong, how it affects the hedging choice or the project cash flows. Written analysis carries professional skills marks.
If the question gives both inflation and interest rates, check which one is wanted. Using the wrong pair is the commonest source of lost marks.
Be ready to compare forecasts from PPP, IRP and the international Fisher effect and explain why the forward rate and the expected spot rate may differ.

Practice questions from Management of international trade and finance

Exchange Rate Determination and Forecasting in other exams

The same ground in other exams, if you are preparing for more than one or want another angle on it.

Exchange Rate Determination and Forecasting: frequently asked questions

What is the difference between PPP and IRP?

PPP uses inflation differences to forecast the future spot rate. IRP uses interest rate differences to set the forward rate. PPP is a long-run tendency and IRP is enforced by arbitrage, so it holds much more closely.

How do I calculate a forward rate using interest rate parity?

Take the spot rate and multiply by (1 + counter currency interest) ÷ (1 + base currency interest). Use rates for the same period as the forward. For a six-month forward, use half the annual rate unless told otherwise.

What is the international Fisher effect formula?

It is S1 ÷ S0 = (1 + ic) ÷ (1 + ib), using nominal interest rates of the counter and base currency countries. For example, if the counter currency rate is 6% and the base rate is 3%, the counter currency is expected to weaken by about 2.9% against the base. It assumes equal real rates.

Is the forward rate a forecast of the future spot rate?

Not exactly. The forward rate is set by interest rate differences and arbitrage. The future spot rate depends on many other factors, so the two often differ, although the forward rate is used as an estimate in some analyses.