Whenever you have a foreign bank account, changes in the currency exchange rates between that country currency and your home currency will cause the value of your foreign currency account to fluctuate. When your local currency weakens relative to the foreign currency, the value of your foreign account increases, creating a currency gain. When your local currency strengthens, your foreign account experiences a loss in real value. Your software can track these fluctuations.

Gains or losses in the value of a foreign account are considered unrealised when the money is still sitting in the foreign account. Conversely, when the money is withdrawn from the account, either by using it to pay for a purchase or by converting it to local currency, the gain or loss is considered realised.