This is a very good question, however, there are many variables to consider.

First, let's address whether the additional people being added to your insurance will qualify as your dependents for tax purposes. The IRS has rules that must be met in order to be considered a dependent. These rules are based on whether the person is your Qualifying Child or your Qualifying Relative. To determine if the tests are met, see Rules for Claiming a Dependent on Your Tax Return .

For the second part of your question, it sounds like the insurance contributions will not be excluded from your gross income. If this is the case, I do not expect your withholding to change unless you have determined that you have dependents.

To determine the amount of withholding based on your circumstances, it is best to use the IRS' Tax Withholding Estimator.