Adding expenses lowers your Adjusted Gross Income. There may be credits or deductions on your return that decrease as your AGI goes down. For example, you need a certain amount of income to qualify for some credits. As your AGI goes down, you may no longer qualify for that credit. Keep in mind that lowering your expenses to allow for a bigger Eared Income Credit is not allowed.
People often don't realize that every entry causes an entire recalculation of your tax return and can often cause unexpected results. The only way to tell what is really happening is to look at and, preferably, to print your 1040 before and after you enter a number.
You can look at your 1040 by clicking on Tax Tools on the left, then Tools. Select View My Tax Summary, then Preview My 1040.
