In November, a company hires three temporary employees that are scheduled to work only the month of December. Those employees work during December, and they are then paid their full salaries in January. In which month should the company record supplies expense?

The reason is that the matching concept and accrual basis says that the expense must be matched with the revenues and must be recorded not when they are paid. They must be recorded when they are incurred.

Now what does this means when we say that the expenses must be recorded when they are incurred not when they are paid?

Suppose it is start of the month and we agreed on terms that you will pay me $10 for each day I will teach you.

I taught you each day and then you paid me my fee in the second month and equal to $600. So when I taught you lessons in the first day, you must record expenses of $10 though you have not paid me. You have taken the benefit from other party and now you legally owe me $10. The other day I taught you again. Now again you owe me another $10 and I legally have the right to receive that money. So incurring cost is receiving the consideration (anything that has a monetary value) from the other party. Now you will record the $10 expenses those day that you are taught lessons.