Can I just file a 1040-ES?
Yes, you can send in a 2012 1040-ES form with a check to cover your tax liability. However, you will likely have to pay penalties for not paying tax in timely fashion as well as interest on the late payment. You can have the IRS figure the penalty and bill you for it, or you can complete Form 2210 (on which these  matters are figured out) yourself and file it with your Form 1040. The long version of Form 2210 often results in the smallest extra amount due but is considerably more time-consuming to complete correctly. Alternatively, if you or your wife have one or more paychecks coming before the end of 2012, it might be possible to file a new W-4 form with the HR Department with a request to withhold additional amounts as Federal income tax. I say might because if the last paycheck of the year will be issued in just a few days' time, it might already have been sent for processing, and HR might tell you it is too late. But, depending on the take-home pay, it might be possible to have the entire $2000 withheld as additional income tax instead of sending in a 1040-ES. The advantage of doing it through withholding is that you are allowed to treat the entire withholding for 2012 as satisfying the timely filing requirements. So, no penalty for late payment even though you had a much bigger chunk withheld in December, and no interest due either.  If you do use this approach, remember that Form W-4 applies until it is replaced with another, and so  HR will continue to withhold the extra amount on your January paychecks as well.  So, file a new W-4 in January to get back to normal withholding. (Fix the extra exemption too so the problem does not recur in 2013).
This is a common occurrence when somebody has multiple jobs in one year. The employer can't know if you have reached the annual limit. They know to stop when you have hit the maximum for their company, but don't have information on the other jobs. In fact the IRS doesn't let them factor in the other jobs. They have to keep making their payment until you hit the max for their company. When you fill out the 1040 there will be a line that checks that the total social security amount for each person was not over the annual limit. The extra will be refunded when you file your taxes. In the future if this happens again you can adjust your withholding to minimize the overage. For the example given in the question to get the 4K extra sooner, increase the number of allowances on the W-4.  You can under withhold federal income tax because you will over withhold social security tax. Many states have a simple method for assessing income tax on nonresidents.  If you have $X income in State A where you claim nonresident status and  $Y income overall, then you owe State A a fraction (X/Y) of the income  tax that would have been due on $Y income had you been a resident of State A.  In other words, compute the state income tax on $Y as per State A rules, and send us (X/Y) of that amount.  If you are a resident of State B, then State B  will tax you on $Y but give you some credit for taxes paid to State A. Thus, you might be required to file a State A income tax return regardless of how small $X is.  As a practical matter, many commercial real-estate  investments are set up as limited partnerships in which most of the annual taxable income is a small amount of portfolio income (usually interest income that you report on Schedule B of Form 1040), and the annual  bottom line is lots of passive losses which the limited partners report (but do not get to deduct) on the Federal return.  As a result, State A is unlikely to come after you for the tax on, say, $100 of interest income each year because it will cost them more to go after you than they will  recover from you. But, when the real estate is sold, there will (hopefully) be a big capital gain, most of which  will be sheltered from Federal tax since the passive losses finally get  to be deducted.  At this point, State A is not only owed a lot of money (it knows nothing of your passive losses etc) but, after it processes the income tax return that you filed for that year, it will likely demand that you file income tax returns for previous years as well. "I've been highly compensated for a while now, and I have never used a tax professional.  My past complications include the year that my company was bought by a VC firm and my stock options and stock held were bought out to the tune of 5x my salary.  And now I have two kids in college, with scholarships, and paying the remainder out of 529 accounts. Usually, I don't even use tax software.  My typical method is to use the online software -- like turbotax online -- and let it figure out where I am.  Then I use the ""Free File Fillable forms"" online to actually complete the process.  Search for ""Free File Fillable Forms"" -- it's not the same as using turbotax or TaxAct for free.   My suggestion to you:  download the PDF form of 1040EZ and 1040A from the IRS.  Print the EZ, and fill it out.  This will give you a better feel for what exactly is going on.  With your income, I don't think you can file the EZ, but it's a good way to get your feet wet. The way income taxes work here in the US: According to the IRS, the Personal Exemption this year is worth $4,050, and the Standard Deduction $6,300, assuming you're single.   Lets assume that your salary will be in fact 75,000, and you don't pay for any benefits, but you do make a 401k contribution of 15% of your salary.  Then your W-2 at the end of the year should tell you to put 63,750 in a particular box on your 1040 form.  (63,750 is 85% of 75,000).  Lets then assume 63,750 is your AGI after other additions and subtractions.  63,750 - 4,050 - 6,300 == 53,400. The federal Tax system is graduated, meaning there are different ranges (brackets) with different percentages.  The term tax people use for taxable income of 53,400 is ""marginal tax rate""...so the last dollar they tax at 25%.  Other dollars less.  According to the IRS, if you're single, then on 53,400, you pay ""$6,897.50 plus 25% of the amount over $50,400""  Or 6897.50 + 750, or 7647.50. Note this is only Federal Income Tax.  You will also be paying Social Security and Medicare payroll Tax.  And I'm guessing you'll also be paying colorado state income tax.  Each state has its own forms and methods for figuring out the taxes and stuff. By the way, when you start, you'll fill out a ""W-4"" form to ""help"" you figure out how much to withhold from every paycheck.  (I find the W-4 is not helpful at all).  Your company will withhold from your paycheck some mysterious amount, and the process of filling out your 1040A or 1040EZ or whatever will be, likely, to get the over-withheld amount back." "Be careful of the other answers here. Many are wrong or partially wrong. The question implies that you knew this, but for everyone else's benefit, you can keep you LLC organization and still elect to be treated as a S-Corp by the IRS just for tax purposes.  You do this by filing Form 2553 with the IRS. (You can also, by the way, elect to be taxed as a ""regular"" C-Corp if you want, although that's probably not advantageous.  See Form 8832.) The advantage of electing to be treated as an S-Corp is that income beyond what constitutes a ""reasonable salary"" are not subject to social security and medicare taxes as they would when paid was wages or counted as self-employment income on Schedule C.  Depending on what you need to pay yourself to meet the ""reasonable salary"" test, your overall income, and other factors about your business, this could result in tax savings. Contrary to other answers here, making this election will not force you to create a board of directors.  You are still an LLC for all purposes except taxes, so whatever requirements you had in organization and governance at the state level will not change.  You will have to file a ""corporate"" tax return on Form 1120S (and likely some corresponding state tax form), so that is additional paperwork, but this ""corporate"" return does not mean the S-Corp pays taxes itself. With a couple of exceptions, the S-Corp pays no taxes directly (and therefore does not pay at the corporate tax rate). Instead the S-Corp apportions its income, expenses, and deductions to the owner(s) on Schedule K.  The owners get their portion reported from the S-Corp on Schedule K1 and then include that on their personal Form 1040 to pay tax at their personal rate. In addition to filing Form 1120S, you will have to handle payroll taxes, which will create some additional administrative work and/or cost. Using a payroll service for this will likely be your best option and not terribly expensive. You've also got the issue of determining your reasonable salary within the rules, which is the subject of other questions on this site and other IRS guidance." First of all, this is a situation when a consultation with a EA working with S-Corporations in California, CA-licensed CPA or tax preparer (California licenses tax preparers as well) is in order. I'm neither of those, and my answer is not a tax advice of any kind. You're looking at schedule CA line 17 (see page 42 in the 540NR booklet). The instructions refer you to form 3885A. You need to read the instructions carefully. California is notorious for not conforming to the Federal tax law. Specifically, to the issue of the interest attributable to investment in S-Corp, I do not know if CA conforms. I couldn't find any sources saying that it doesn't, but then again - I'm not a professional. It may be that there's an obscure provision invalidating this deduction, living in California myself - I wouldn't be surprised. So I suggest hiring a CA-licensed tax preparer to do this tax return for you, at least for the first year. Yes, you do. Depending on your country's laws and regulations, since you're not an employee but a self employed, you're likely to be required to file some kind of a tax return with your country's tax authority, and pay the income taxes on the money you earn. You'll have to tell us more about the situation, at least let us know what country you're in, for more information. What I'm going to write is far too long for a comment, so I'll put it here even though its not an answer. That's the closest thing to an answer you'll get here, I'm afraid. I'm not a tax professional, and you cannot rely on anything I say, as you undoubtedly know. But I'll give you some pointers. Things you should be researching when you have international clients: Check if Sec. 402 can apply to the pension funds, if so your life may become much easier. If not, and you have no idea what you're doing - consider referring the client elsewhere. You can end up with quite a liability suit if you make a mistake here, because the penalties on not filing the right piece of paper are enormous. You need to file IRS Form 1040-NR. The IRS's website provides instructions.