Math....ah....matician?

I was doing the budget this morning....with the new month around the corner and all. I suck at math, which even makes this funnier. But I was subtracting bills and ended with a number a lot lower than planned and FREAKED OUT! I was so paranoid I had Scott re-do the math and it was right. I kept looking at mine and looking at his....could not figure it out. We double checked which bills we are paying, the amounts...everything.  Finally we realized that I was subtracting it from the wrong number. ugh!