My boyfriend is claiming 3 and is wonder if there is some kind of formula to tell how much money he is going to get back on his taxes, or if there is not enough being taken out and he needs to change it to claim less. Does anyone know where I can find any information to help him?

Circular E has all the withholding tables based on every conceivable payment plan, from daily to monthly pay.

You can download Circular E from Internal Revenue Service.