Your net check is kind of a misnomer. Your ultimate net pay can only be determined after you determine your gross income for the year. Your annual net income is computed after the annual taxes have been computed. Annual taxes are base on your "tax bracket" or how much your taxable income is. There are also social security and medicare taxes.
If during the year, your withholding is small, making your net paycheck big, you may owe more taxes in April with your annual tax retrun. (1040) If during the year, your withholding is bigger, your net paycheck will be smaller, but you will have a smaller payment due or a bigger refund in April.
That's the simplest, I can make it. Sorry.