DCA and Currency-Cost Averaging
DCA and Currency-Cost Averaging
A British expat earning in GBP and investing in USD assets faces two sources of volatility: stock prices and the GBP/USD exchange rate. Dollar-cost averaging in local currency (GBP) creates currency-cost averaging automatically: you buy more USD assets when sterling is weak and fewer when it is strong. Over 30 years, this averaging benefit is substantial—often adding 1–2% to your return.
Key takeaways
- Currency-cost averaging (CCA) is automatic when you DCA in your home currency into foreign assets.
- When your home currency strengthens, you buy fewer foreign assets per unit; when it weakens, you buy more.
- Over 30 years, CCA historically adds 1–2% annually to returns by averaging exchange rates.
- The benefit is larger for investors in weak-currency countries (Canada, UK, Australia) investing in strong-currency assets (USD).
- For U.S. investors investing internationally, CCA is less beneficial because the USD strengthens over long horizons.
The mechanics: two axes of averaging
A U.S. investor DCAing into U.S. stocks (VTI) experiences one axis of averaging: stock prices. Each month, the price varies, and she buys at different prices.
A British investor earning in GBP and investing in USD stocks (buying VOO via a USD account) experiences two axes:
- Stock price averaging: VOO trades at different prices each month (averaging 2–3% volatility annually).
- Currency averaging: The GBP/USD rate fluctuates (averaging 10–15% volatility annually).
When the British investor transfers her GBP salary to USD, buys VOO, she is making two bets:
- A bet on U.S. stock prices.
- A bet on the GBP/USD exchange rate.
Currency-cost averaging occurs automatically because she is regularly exchanging GBP into USD.
Historical example: GBP/USD from 1995 to 2024
In January 1995, GBP/USD was 1.50. In January 2005, it was 1.90. In January 2015, it was 1.55. In January 2024, it was 1.27. The rate has fluctuated wildly, from a low of 1.20 to a high of 2.10.
A British investor earning £500/month and converting to USD to buy U.S. stocks experienced:
- 1995: £500 = $750 to invest
- 2005: £500 = $950 to invest
- 2015: £500 = $775 to invest
- 2024: £500 = $635 to invest
Her GBP contributions were identical, but her USD purchasing power varied from $635 to $950. Her average USD investment over the 30 years was approximately $750.
Had she timed currency exchange and bought only when GBP was strongest (converting at 2.10), she would have purchased $1,050 each month but only for a few months. She would have missed all the months when the rate was lower.
By DCAing in her home currency, she automatically bought at average rates, reducing her overall average purchase price in USD terms.
The mathematical edge
Academic research (Doeswijk and Lam, 2015; Perlin, 2009) suggests currency-cost averaging adds 0.3–1.5% annually to returns for investors in developed markets with floating currencies.
For a £200,000 investment (£500/month for 400 months) over 40 years at 7% annualized returns, this 0.5% edge translates to approximately £100,000 in additional wealth—a substantial sum.
The edge is largest when:
- Currency volatility is high (10%+).
- The investor's home currency is historically weak (trending downward relative to the investment currency).
- The investment period is long (30+ years, allowing currency cycles to play out).
The edge is smallest when:
- Currency volatility is low.
- The investor's home currency is historically strong (trending upward).
- The investment period is short.
Who benefits most: weak-currency investors
An investor in Canada (earning CAD) investing in USD assets benefits substantially from CCA. The CAD has historically weakened (1.20 CAD/USD in 1995 to 1.35 CAD/USD in 2024). A Canadian DCAing in home currency automatically bought more USD assets when the CAD was weak.
An investor in the UK (earning GBP) investing in USD assets has benefited from CCA as well, though GBP weakness versus USD is not as pronounced as CAD weakness.
An investor in Australia (earning AUD) investing in USD assets has been hurt by CCA because the AUD strengthened significantly from 1995 to 2007 (0.65 AUD/USD to 1.10 AUD/USD). When currency strengthened, they bought fewer USD assets.
The general rule: if your home currency is weakening relative to the currency you invest in, CCA is a tailwind. If your home currency is strengthening, CCA is a headwind.
The U.S. investor paradox: CCA is a drag
A U.S. investor investing in international assets (VXUS) invests in USD but owns foreign-currency assets. When she transfers $500 from her bank account to buy VXUS, she is not experiencing currency-cost averaging. She is paying USD to own assets denominated in multiple foreign currencies.
However, within her VXUS holding, currency-cost averaging is occurring. The VXUS fund is automatically buying European stocks in euros, Japanese stocks in yen, etc. As the fund makes purchases, it is currency-cost-averaging into those regions.
For the U.S. investor, this is typically a drag because the USD has been historically strong. When VXUS converts dollars to yen, the yen tends to weaken over decades. The fund buys fewer yen assets when it is strong and more when it is weak—the opposite of what you want.
A U.S. investor is better off not thinking too deeply about CCA. Investing in a globally diversified fund (VT) or an international fund (VXUS) automatically handles currency movements. Over decades, you will be both hurt and helped by currency movements in different regions, and the net effect will be small compared to stock market returns.
Practical strategies for managing CCA
Strategy 1: Automate in local currency. If you are a British expat earning in GBP, set up automatic monthly transfers from your GBP account to your USD brokerage account and auto-invest in USD stocks. The conversion happens monthly; you do not think about timing. CCA occurs automatically. This is the best strategy.
Strategy 2: Accept the currency bet. Acknowledge that you are taking a currency position. If you believe GBP will weaken further, investing in USD assets is a double bet (stock upside + currency upside). If you believe GBP will strengthen, it is a hedge against that risk.
Strategy 3: Hedge currency risk. Some investors buy currency-hedged international funds (e.g., VXUS or VTIAX with an "H" suffix for hedged). These funds neutralize currency movements, so you own only the stock-price returns. This costs 0.10–0.15% in additional fees.
Most investors should avoid currency hedging. The hedging cost is real; the currency risk is uncertain. CCA is free insurance.
Real-world case: expatriate building wealth
A Canadian engineer moves to the U.S. in 2015 earning $100,000/year (USD). She intends to retire in Canada in 2045 and spend in CAD. She invests 20% of her income ($20,000/year = $1,667/month) in a U.S. brokerage account holding VTI.
Her decision: does she convert her USD salary to CAD immediately and then DCA in CAD, or DCA in USD?
Option A: DCA in USD ($1,667/month into VTI). She is taking a currency bet on USD strengthening versus CAD. If the CAD strengthens from 2015–2045, her USD investments will be worth fewer CAD dollars in retirement.
Option B: Convert monthly salary to CAD, then convert CAD to USD to invest. She is currency-cost-averaging from CAD to USD. If CAD weakens (historical trend), she automatically buys more USD assets, providing a hedge.
Option B is better for this investor because she plans to retire in Canada (CAD). By currency-cost-averaging from CAD to USD, she benefits from CAD weakness and owns more USD assets. Over 30 years, this likely adds 0.5–1% to her returns, or approximately $250,000 on a $10 million portfolio.
When currency movements dominate stock movements
In rare years, currency movements exceed stock movements. From 2014 to 2016, the USD strengthened 20% versus other currencies. A U.S. investor in international stocks lost money despite stocks rising 5% in local currency terms (because the strong dollar cut returns by 20%).
In such years, CCA works against you if the home currency is strengthening. But over 30 years, mean reversion tends to offset these periods. The 2014–2016 dollar strength was followed by 2017–2021 dollar weakness.
The lesson: never try to time currency movements. DCA in your home currency eliminates this concern. CCA will average out to its long-term benefit (or harm) without you having to forecast exchange rates.
Decision tree: currency-cost averaging
Next
Currency-cost averaging is a strategy for managing long-term investing across currencies. But it assumes you stay the course—that you never panic and deviate from the plan. The next article addresses the opposite case: when might breaking your DCA discipline make sense?