Help with validation Rule

Hello there!

I'm having troubles with a validation rule and maybe someone can give me some advice or support.

I have three fields for Budget planing. 

• Field 1 (Total Budget) indicates the total available Budget. 
• Field 2 (Amount spent) indicates the total amount that will be spent. 
• Field 3 (Remaining Budget) indicates the total remaining Budget.

So, I have created an easy validation rule, that restricts the Field 2 to be greater than Field 1. 

Field 2 >= Field 1

Logic, right? But now I'm having the problem, that I get an error message from the system if I try to spent the total available budget, so that Field 3 could be = 0 EUR. So, to avoid the validation error, I have to safe 1 EUR. 

In conclusion, I need to be able to spent all the Budget without exceeding the available amount, but no more... So why? What I'm missing?

Thanks in advance for your support :) 

#Validation Rule