Pretty good looking application, clean look and very easy to use. Great work!
If you want to ‘complicate’ things a little bit I have an idea for your application
Add multiples currencies to the application (USD, CAD, EURO, REAL, etc) to allow the user to add entries in different currencies, then use an free API to make conversions.
For example, I’m Portuguese I use EURO, but imagine that I go on a travel to USA and I want to add the expenses of that travel to the application and they are all in USD. Then in the end of the month if I want to check my balance you use the API to convert all the entries in a single currency and show the final value.
This is just an idea how you can improve it Good Job