Can I up my deductions if I overpaid tax the first six months of the year

You can submit a new W4 any time to your employer to increase the number of allowances, which will reduce your withholding. Just be sure to follow the directions, and remember that when you sign the form you are certifying that your representation of the number of allowances is accurate. Even if you had more taxes withheld than necessary for the first 6 months, your goal should be to get it right going forward.

How do you know you over-paid for the first 6 months?

QUOTE," . . . if I overpaid tax the first six months of the year . . ."--Right! Exactly. How do you know that you already overpaid your tax the first six months of the year, bud?? In general, you don't know it till you pay the whole of your estimated quarterly taxes as an employer(SECA Taxes) or FICA and other FIT & SIT withheld by your employer as an employee and comare the amount to the amount of your tax liaiblity on your 1040. If the amount of taxes withheld exceeds the amount of your 1040, the result will be tax refund due to overpayment!!