I have wanted this feature for a LONG time — it would be a HUGE quality of life improvement. Please please please can we have simple math functions in the amount field, .e.g., I want to be able to type the following types of things into the amount field:
1.23 + 4.56
1.23 - 4.56
9.99 * 1.0825
123.45 / 2
If the result of the math function is a negative number (example #2), then it just has to toggle the income/expense type of the entry. This all only needs to happen on the client side, i.e., you only need to store the end result of the function upon save, not the equation that the user typed in.