My husband recently got a job and will be making about 50K a year. This is the first year that he is the primary income for the household. We have 2 kids, who are in daycare, and I do not have a job, I do hawever, receive about 500/mth from a pension account of my deceased father's.

I am currently in school getting my masters, and want us to receive the most that we can from his check monthly WITHOUT having to pay at the end of the year.

Should we claim 4 or 6?

If you follow the directions on the W4 (see: http://www.irs.gov/pub/irs-pdf/fw4.pdf ), it seems you should claim 5 allowances:

A. One for your husband
B. Zero - as your $6K/year additional income is like a you having a job
C. One for you
D. Two for the kids as dependents
F. One for day care expenses (assuming you pay > $1800/year)

I suggest you try this for a year, and if need be he can always submit a new W4 next year if he needs to make adjustments. As an alternative, he could claim 6 allowances (adding one more under item B), and then you could submit quarterly estimated payments to cover the expected taxes on your $6K additional income.