Holding value changes: separate local price and FX
A foreign-currency stock’s reporting-currency value changes with both its local price and the conversion rate. Hold the quantity fixed to isolate those effects, then add trades and cash flows separately. Otherwise, a larger position can be misread as a price gain or a currency move can be attributed to business performance.
Define the valuation inputs
Investor.gov’s statement guide explains account holdings and valuation-related information. The account’s actual price, quantity and currency records are the evidence for a reconstruction. IFRS 7 financial-instrument risk disclosures concern company exposures and should not be mistaken for the investor’s own account translation calculation.
Specify the reporting currency and quote the exchange rate as reporting-currency units per local unit. Reversing that convention reverses the arithmetic. Record price and FX timestamps, especially when local markets close at different times. The worksheet is an observation bridge, not a tradable synchronized price.
Hypothetical fixed holding
Assume 100 shares begin at a local price of 50 and an exchange rate of 0.20. Reporting value is 1,000. At the second observation, local price is 55 and the exchange rate is 0.18. Reporting value is 100 × 55 × 0.18 = 990, down 10 despite a local price increase.
One exact additive bridge uses starting inputs for the first-order effects and a separate interaction:
| Valuation component | Formula | Amount |
|---|---|---|
| Local-price effect | 100 × (55 − 50) × 0.20 | +100 |
| FX effect | 100 × 50 × (0.18 − 0.20) | −100 |
| Interaction | 100 × (55 − 50) × (0.18 − 0.20) | −10 |
| Total value change | Sum of three components | −10 |
The interaction is necessary because both price and currency changed. A sequential bridge can instead assign the interaction to whichever factor is applied second, but its ordering must be stated. Do not compare attribution labels from different conventions as though their individual components must match.
Keep transactions outside the fixed-quantity test
If twenty shares are purchased between observations, the quantity no longer remains fixed. Record the cash purchase and its actual date separately, then use an appropriate holding-value movement schedule. Multiplying the new quantity by the old price difference can assign gains to shares not owned during the full interval.
Likewise, dividends are cash events unless reinvested. A price-only bridge excludes those receipts. Calling its result total return would be inaccurate. Split adjustments and other corporate actions require consistent quantity and price units before any attribution is meaningful.
Interpret the two currency layers
The account conversion describes the investor’s reporting lens. The company may also have operating currency effects in its own revenue, costs and debt. Those effects can influence local share prices but are not separately identified by this algebra. Do not label the full local-price movement “fundamental performance.”
For a portfolio containing several currencies, calculate each holding with its own verified rate and aggregate reporting-currency amounts. Preserve missing or stale quotes rather than filling them with an arbitrary rate. A reported loss can combine local gains and currency weakness, but the bridge does not establish why either market moved.
The completed worksheet should state timestamps, rate direction, quantity assumptions, treatment of flows and attribution convention. It supports explanation and record checking, not currency forecasting, tax gain calculation or a recommendation to hedge.
FAQ
Can local-price and FX percentage changes simply be added?
Only as an approximation. The exact combined percentage includes their product, just as the value bridge includes an interaction term.
Does a positive local return guarantee a reporting-currency gain?
No. A weaker local currency can offset or exceed the local-price increase, as the hypothetical calculation illustrates.