Currency effect calculator
This calculator shows how much of a change in an account's value came from the exchange rate and how much from the balance itself. Say you live in the UK and a US account went from USD 10,000 to USD 10,500 over six months. If the dollar fell in the meantime, the account can still be worth fewer pounds than before.
Enter the balance and the exchange rate on two dates, and you'll get the currency effect and the balance change. The two always add up to the total change.
Split a change into currency and balance
Nothing you enter here is saved or sent anywhere.
How to read the result
The currency effect is the change in value of the balance you started with that comes from the exchange rate moving, even if you didn't touch the account.
The balance change covers everything that happened inside the account, such as deposits, withdrawals, interest and market moves in a brokerage, valued at the end rate.
If the account is in the same currency as your display currency, the currency effect is zero.
Debts work the other way round. If you owe EUR 50,000 and the euro falls against the pound, the debt is worth fewer pounds, so the currency effect is positive.
Where to get the rates
Use the same source for both dates. A bank's conversion rate includes a margin, so it's a little worse than a published reference rate. For valuing an account the reference rate is the better choice, while your bank's rate is what you'd actually get if you converted today.
If your source quotes the rate the other way round (dollars per pound instead of pounds per dollar), divide 1 by it first. For example, 1.25 dollars per pound is 0.80 pounds per dollar.
The method
- Currency effect = balance at start × (end rate − start rate)
- Balance change = (balance at end − balance at start) × end rate
Together they add up exactly to the end value minus the start value.
Other methods split the change a little differently, for example by valuing new money at the old rate. This calculator uses the same method as Thallo, so you'll get the same figures in both.
A worked example
Here the display currency is GBP and the account is in US dollars.
| Start | End | |
|---|---|---|
| Balance | USD 10,000 | USD 10,500 |
| Rate (GBP per 1 USD) | 0.80 | 0.76 |
| Value in GBP | GBP 8,000 | GBP 7,980 |
Total change: −GBP 20.
- Currency effect: 10,000 × (0.76 − 0.80) = −GBP 400
- Balance change: (10,500 − 10,000) × 0.76 = +GBP 380
Adding them up gives −400 + 380 = −20. The extra USD 500 is worth GBP 380 at the end rate, but the weaker dollar took GBP 400 off the value of the USD 10,000 you started with.
Several accounts
The calculator works on one account at a time, so for several accounts you can run it once for each and add up the results. The guide on why your net worth changed when you didn't do anything works through a three-account example with accounts in Danish kroner, US dollars and Thai baht.
In Thallo, What moved does this for all your accounts at once, for any two dates, using exchange rates fetched every day. You type in the balances, and the currency effect is shown for each currency and the balance changes for each account.
Start free, and once your accounts are in, pick any two dates to compare.