The Internal Revenue Service has offered answers to the four most frequently asked questions about Estimated Tax, they are:

1. Is an S-Corporation required to pay quarterly estimated tax?

Rarely does an S corporation make estimated tax payments.

An S Corporation must make installment payments of estimated tax if the total of these taxes is $500 or more:

The tax on certain capital gains,
The tax on built-in gains,
The excess net passive income tax, and
The investment recapture tax.

2. How do I know if I have to file quarterly individual estimated tax payments?

If you owed additional tax for the prior tax year, you may have to make estimated tax payments for the current tax year.

You must make estimated tax payments for the current tax year if both of the following apply:

You expect to owe at least $1,000 in tax for the current tax year, after subtracting your withholding and credits.
You expect your withholding and credits to be less than the smaller of:
90% of the tax to be shown on your current year’s tax return, or
100% of the tax shown on your prior year’s tax return. (Your prior year tax return must cover all 12 months.)
There are special rules for:

Certain taxpayers with higher adjusted gross income
Farmers and commercial fishermen
Aliens
Estates and Trusts

3. Do self-employment taxes need to be paid quarterly or yearly?

If you are required to make estimated tax payments, self-employment tax is paid by making quarterly estimated tax payments which include both income tax and social security tax.

4. When are the quarterly estimated tax returns due?

You only make estimated tax payments using payment vouchers. There is not an estimated tax return.
Your first estimated tax payment is usually due the 15th of April.
You may pay the entire year’s estimated tax at that time, or
You may pay your estimated tax in four payments that are due April 15th, June 15th, September 15th, and January 15th of the following year.
If the due date for making an estimated tax payment falls on a Saturday, Sunday, or legal holiday, the payment will be on time if you make it on the next day that is not a Saturday, Sunday, or legal holiday.

If you have a specific question about your Federal Tax return you can call the IRS and receive Live Telephone Assistance. Here are the particulars:

Telephone Assistance for Individuals:
Toll-Free, 1-800-829-1040
Hours of Operation: Monday – Friday, 7:00 a.m. – 10:00 p.m. your local time (Alaska & Hawaii follow Pacific Time).

Telephone Assistance for Businesses:
Toll-Free, 1-800-829-4933
Hours of Operation: Monday – Friday, 7:00 a.m. – 10:00 p.m. your local time (Alaska & Hawaii follow Pacific Time).

source: irs.gov

Do you have questions about IRS Filing Status, Exemptions or Dependents?  Here are 6 of the most frequently asked questions taxpayer have about these issues.

1. How much does a student have to make before he or she has to file an income tax return?

If you are an unmarried dependent, you must file a tax return if your earned and/or unearned income exceeds certain limits.

To find these limits refer to Filing Requirements for Dependents in Publication 501, Exemptions, Standard Deduction and Filing Information.
Even if you do not have to file, you should file a federal income tax return to get money back if any of the following apply:
You had income tax withheld from your pay.
You qualify for the earned income credit.
You qualify for the additional child tax credit.

2. For head of household filing status, do you have to claim a child as a dependent to qualify?

In certain circumstances, you do not need to claim the child as a dependent to qualify for head of household filing status, such as when the qualifying child is unmarried and is your child, grandchild, stepchild, or adopted child.

3. Is there an age limit on claiming my children as dependents?

Age is a factor in the qualifying child test, but a qualifying relative can be any age.

As long as the following dependency exemption tests are met, you may claim him or her:

Qualifying child or qualifying relative test
Dependent taxpayer test
Citizenship or resident test
Joint return test

4. My wife and I are married filing separately. We have one son and we meet all of the dependency exemption tests. We contributed an equal amount to our son’s support and want to know if we both can claim him on our separate returns?

A dependency exemption may only be claimed on one return.

Since your son is a qualifying child for both of you, you and your wife can decide who will claim the child.
A multiple support declaration identifying each of the others who agreed not to claim the exemption must be attached to the return of the person claiming the exemption. Form 2120, Multiple Support Declaration, can be used for this purpose.
If you cannot agree on who will claim him refer to Tie-Breaker Rule in Publication 501, Exemptions, Standard Deduction, and Filling Information.

5. If you pay child support, are you allowed to deduct anything on your taxes or claim the child as an exemption?

Nothing can be deducted for the child support payments.

Child support payments are neither deductible by the payer nor taxable income to the payee.
You may be able to claim the child as a dependent.

The parent who the child lived with for the greater part of the year is the custodial parent. 
Generally the custodial parent is allowed to claim the exemption for the child if the other exemption tests are met.
The noncustodial parent may be allowed to claim the exemption for the child if the custodial parent signs a Form 8332 (PDF), Release of Claim to Exemption for Child of Divorced of Separated Parents, or a substantially similar statement.

6. If I claim my daughter as a dependent because she is a full-time college student, can she claim herself as a dependent when she files her return?

If you claim your daughter as a dependent on your income tax return, she cannot claim herself on her income tax return.

If an individual is filing his or her own tax return, and the individual can be claimed as a dependent on someone else’s return, the individual cannot claim his or her own personal exemption.
In this case, your daughter should check the box on her return indicating that someone else can claim her as a dependent.

Federal Tax Laws are complex and may require that you speak with a Tax Expert, CPA, go online to the irs.gov site or even speak to someone at the irs.  Here are some toll free numbers to speak with an IRS tax representative:

IRS Telephone Assistance for Individuals:
Toll-Free, 1-800-829-1040 
Hours of Operation: Monday – Friday, 7:00 a.m. – 10:00 p.m. your local time (Alaska & Hawaii follow Pacific Time).

IRS Telephone Assistance for Businesses:
Toll-Free, 1-800-829-4933
Hours of Operation: Monday – Friday, 7:00 a.m. – 10:00 p.m. your local time (Alaska & Hawaii follow Pacific Time).

source: irs.gov