You may end up needing to pay more than that. I generally find it best to use the irs withholding calculator. They generally make it available about February of the current year. If you do it with your most recent paystubs, it can calculate what you will owe in taxes, how much will be withheld and tell you what to set your w4 for both jobs.
https://apps.irs.gov/app/withholdingcalculator/index.jsp
