I am totally blowing my budget this month, and I came at the damage from both directions.
On the income side, I decreased my income by not taking any call in the last pay period - an accidental oversight. I wasn't going to have any this pay period either, luckily someone was willing to give a shift away. Next, I went home several hours early one day when things were slow and elected to take the time off without pay because I have a vacation coming up and didn't want to burn any extra PTO.
On the expenditure side, I neglected to realize that because the bank changed one of my accounts due to a data compromise, that my cell phone bill stopped getting paid automatically. I don't open those statements in a timely manner since they are automatic and I ended up having to pay for three months at once. Then I signed up for a class in cartoneria (Mexican paper mache) which I wasn't planning on because I didn't know it existed. This year's Halloween theme (we go all out with Halloween decorating) is Dia De Los Muertos and I was going to try to figure out how to do the paper mache on my own but now I don't have to and this is (for me) a justified expense that I am willing to pay for (and if you knew how excited I get about Halloween you would agree).
Ultimately, there has to be some flexibility in any budget for inevitable ups and downs. I keep some slush money for budget overruns and fortunately have the ability to increase my income by picking up extra call shifts on occasion. I have a system and I know it works for me. If I couldn't make extra money I'd have to come up with a different system.
This has also been a lesson in diligence. I shouldn't be waiting over three months to check on bill payment.