Each Kitty has a currency that is specified on Kitty creation. We call it the home currency. Expenses and debts are all displayed in that currency.
If you want to work with multiple currencies in a Kitty (for example, because you're on an international trip) then you need to upgrade your Kitty first. Afterwards, you can add expenses in any currency you want and Kittysplit will convert the amount back to your home currency. All debts will be displayed in your home currency.
We fetch the exchange rates from swop.cx, a simple and lightweight internet service for current and historical foreign exchange (forex) rates. To make it as fair as possible, we fetch the exchange rate for the given date of the expense, which we feel is rather smart 🤓. Editing an expense will only change the rate if the date changes too. We keep the most current rates for all currencies and a refresh every 12 hours.
You can change the home currency at any time. In a regular Kitty, all expenses simply switch to the new currency, without converting the amounts. In a Super Kitty, all expenses are converted with the exchange rate of their date, and all debts are recalculated. Only the person who created the Super Kitty can do this. Custom exchange rates are reset to the automatic rate, but we'll ask you first.