I already filed a federal extension a few days but I was just informed that I will owe more tax than I originally calculated. Two questions:

1) How do I pay the additional amount, since I already filed my extension?

2) Where do I input this additional amount on my actual 1040 when I end up filing in a few months?

1) you have met your filing requirements until October 15, 2014 but NOT your payment obligations ias you owe taxes.aslongas you owe taxes to irs, paying late will not pay off, even if you have an accepted extension. IRS penalties and interest will still accrue, based on the amount you owe.nedless to say, as you do owe taxes, interest and penalties will add up until you pay your balance due. You can choose your payment options; To avoid late payment penalties, you should pay your balance due or set up an alternate arrangement. If You DON'T Have the Funds to Pay Your Taxes. You may use Short-Term Extension of Time to Pay. If you will be able to pay your balance due within 120 days, you can call the IRS to see if you can qualify for a short-term extension of time to pay. If you owe no more than $50,000, you may qualify for an installment agreement with the IRS.please contact the irs for more info.


2) if you are a self employer, then,you are not subject to withholding and thus are required to make quarterly estimated tax payments. The IRS charges an estimated tax penalty to taxpayers who underpay their estimated tax. You need to call the IRS at (800) 829-1040 to determine the exact amount of your estimated tax penalty. You may request that they calculate any additional interest charges, which the IRS may add to the balance due caused by the penalty.



if you are an EE with W2, then, as you are anEE, your employer probably withholds income tax from your pay. The amount withheld is paid to the IRS in your name. Estimated tax is used to pay not only income tax aslongaslity your tax withheld from your paychecks is lower than the tax liab
on 1040. If you do not pay enough tax through either withholding or estimated tax by the due date of each payment, the IRS may charge you a penalty. You can increase your withholding on your W-2 income, but keep in mind that it's too late to do this for the 2013 tax yea. please visit the irs website here;
2014 Withholding Calculator