Similar to a feature YNAB had - when editing a budgeted amount I can add or subtract a value, rather than reset the budget entirely.

Example: my budget for a specific category is at $503.68, and I would like to add $115.00 to it. I could click '+' and enter $115 to update the total, rather than having to do the math myself and enter $618.68. The case is analogous for subtracting an amount from the budget.