# What are good criteria to decide how much money I should keep in a foreign exchange credit card account?

### The Situation

I have a Wise account for EUR and AUD.

Into the Wise AUD account I can easily (without fees) put money from an AUD bank account when needed. For most of my purchases I use the AUD account, but some online purchases I should pay with my EUR account in order to avoid conversion fees.

Now, I have received a larger amount in the EUR account which I won't us up in a year. So it makes sense to move the money (via the Wise AUD account) out of Wise into a an normal savings account to get some interest. But as said for some money it might make sense to be kept in the EUR account for the occasional case of low-amount online purchases in foreign Europe.

### My Question

How can I create an easy way (algorithm/formula) to decide much money I should keep in the Wise EUR account?

### Specific information

• Interest rate of the AUD savings account: 1.35% p.a

• Past purchases per year on the EUR account (as prediction): EUR 250

• EUR amount in Wise account: EUR 3000

• Wise fee per transfer out of Wise: approx. AUD 0.80.

• Wise exchange rate: 1 EUR = 1.58 AUD plus approx. 0.4% fee

This means: Let's say I transfer

2,000 EUR.

Then I will at the end have

(2000 - 0.4%) * 1.58 - 0.8 = 3,146 AUD

transferred into my AUD Savings account.